Liquid crystal display device with improved field angles

ABSTRACT

The liquid crystal display device of this invention includes: a liquid crystal display element including a pair of substrates, a liquid crystal layer interposed between the pair of substrates, and an alignment film formed on a surface of at least one of the pair of substrates facing the liquid crystal layer; a pair of polarizers disposed on both surfaces of the liquid crystal element to sandwich the liquid crystal element; and at least one optical phase element disposed between at least one of the pair of polarizers and the liquid crystal element, wherein three principal refractive indices na, nb, and nc of an index ellipsoid of the optical phase element have the relationship of na=nc&gt;nb, a direction of the principal refractive index nb is tilted clockwise or counterclockwise from the normal of a surface of the optical phase element with respect to a direction of one of the principal refractive indices na and nc which is substantially parallel to the surface of the optical phase element as an axis, and a direction of the other principal refractive index nc or na is tilted clockwise or counterclockwise from a direction substantially parallel to the surface of the optical phase element, and at least one of rates of variation of an ordinary refractive index no and an extraordinary refractive index ne of a liquid crystal material of the liquid crystal layer with respect to a wavelength is set in a range in which viewing angle dependent coloring does not occur on a screen.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid crystal display devicein which the angle of field of the display screen has been improved bycombining a liquid crystal display element with a phase element havingoptical anisotropy.

[0003] 2. Description of the Related Art

[0004] Conventionally, liquid crystal display devices (hereinafter,referred to as LCD devices) using a nematic liquid crystal material havebeen broadly used as numeral segmented type display devices for watches,clocks, portable calculators, and the like. In recent years, such LCDdevices have found applications in broader fields, as display devicesfor wordprocessors, notebook type personal computers, and the like, aswell as liquid crystal monitors for car navigation systems, and thelike, for example.

[0005] An LCD device of this type includes a pair of light transparentsubstrates arranged to face each other with a liquid crystal layerinterposed therebetween. Electrodes and interconnections for activatingand inactivating pixels are formed on the substrates. For example, in anactive matrix LCD device, pixel electrodes are arranged in a matrix onone of the substrates for applying a voltage to the liquid crystallayer. Active elements such as field effect transistors are provided onthe same substrate together with interconnections as switching means forselectively applying the voltage to the respective pixel electrodes. Ina color LCD device, a color filter layer composed of color filters ofred, green, and blue, for example, is disposed on one of the substrates.

[0006] In such LCD devices, different display modes are appropriatelyselected depending on the twist angle of a nematic liquid crystalmaterial used. Among such display modes, an active driving type twistednematic liquid crystal display mode (hereinafter, referred to as a TNmode) and a multiplex driving type super-twisted nematic liquid crystaldisplay mode (hereinafter, referred to as an STN mode) are well known.

[0007] In the TN mode, nematic liquid crystal molecules are oriented ina state twisted 90° between the pair of substrates, so that light isguided along the twisted direction. In the STN mode, the twist angle ofnematic liquid crystal molecules is made greater than 90°, so that thelight transmittance of the liquid crystal layer exhibits a sharp changewhen a voltage near a threshold voltage is applied.

[0008] Since the STN mode utilizes the birefringence effect of a liquidcrystal material, the background of the display screen is likely to beuniquely colored due to color interference. In order to effectmonochrome display in the STN mode without an occurrence of suchcoloring, using an optical compensation plate is conventionallyconsidered effective. Two display modes using such an opticalcompensation plate are known; a double super-twisted nematic phasecompensation mode (hereinafter, referred to as a DSTN mode) and a filmtype phase compensation mode (hereinafter, referred to as a film-addedmode).

[0009] In the DSTN mode, the LCD device includes two liquid crystalcells, i.e., a liquid crystal cell for display and a liquid crystal cellin which liquid crystal molecules are twisted at an angle reverse tothat in the liquid crystal cell for display. In the film-added mode, afilm having optical anisotropy is provided. The film-added mode isconsidered advantageous since it is light in weight and low in cost.

[0010] By employing any of the above phase compensation modes, the LCDdevices of the STN mode have been improved in the monochrome displaycharacteristics. Accordingly, a color STN LCD device provided with acolor filter layer has been realized as a color display.

[0011] The TN mode is roughly classified into a normally-black mode anda normally-white mode.

[0012] In the normally-black mode, a pair of polarizing plates aredisposed, sandwiching a liquid crystal display element (hereinafter,referred to as an LCD element) therebetween, so that the polarizingdirections thereof are parallel to each other. In this mode, black isdisplayed when no voltage is applied to the liquid crystal layer. In thenormally-white mode, a pair of polarizing plates are disposed,sandwiching an LCD element therebetween, so that the polarizingdirections thereof are orthogonal to each other. In this mode, white isdisplayed when no voltage is applied to the liquid crystal layer. Thenormally-white mode is advantageous when display contrast, colorreproducibility, viewing angle dependence of display, and the like aretaken into consideration.

[0013] The TN mode LCD device has viewing angle dependence in which thecontrast of display images is changed or inverted depending on thedirection in which and the angle at which an observer views the displayscreen. This occurs because liquid crystal molecules have refractiveindex anisotropy An and they are oriented in a tilted state with respectto the upper and lower substrates. As a result, a viewing anglecharacteristic of a wide angle of field is not obtained. This problemwill be described below in detail.

[0014]FIG. 21 schematically illustrates a cross-sectional structure ofan LCD element 31 of the TN mode. With an application of a voltage to aliquid crystal layer for gray scale display, liquid crystal molecules 32are in a state of slight rise.

[0015] In the LCD element 31, a linear polarized light beam 35 passingthrough the element in a direction normal to the surfaces of a pair ofsubstrates 33 and 34 and linear polarized light beams 36 and 37 passingthrough the element in directions tilted from the normal are incident onthe respective liquid crystal molecules 32 at different angles from eachother. Since the liquid crystal molecules 32 have refractive indexanisotropy An as described above, ordinary light and extraordinary lightare generated when each of the linear polarized light beams 35, 36, and37 passes through the liquid crystal molecules 32. As a result, thelinear polarized light beam is changed to an elliptic polarized lightbeam due to the phase difference between the ordinary light and theextraordinary light. This is a cause of the occurrence of viewing angledependence.

[0016] Moreover, in an actual liquid crystal layer, the tilt angle ofthe liquid crystal molecules 32 located in the middle of the liquidcrystal layer between the substrates 33 and 34 is different from that ofthe liquid crystal molecules 32 located in the vicinity of thesubstrates 33 and 34. Also, the liquid crystal molecules 32 are twisted90° around the normal of the substrate surface as an axis. These arealso causes of the occurrence of the viewing angle dependence.

[0017] Thus, the linear polarizes light beams 35, 36, and 37 passingthrough the liquid crystal layer are caused to have variousbirefringence effects depending on the directions and angles thereof.This results in the generation of complicated viewing angle dependence.

[0018] For example, when the viewing angle is gradually tilted from thedirection normal to the screen in the positive viewing direction (towardthe lower side of the screen), a phenomenon in which the display screenis colored (hereinafter, referred to as a coloring phenomenon) and aphenomenon where black and white are inverted (hereinafter referred toas an inversion phenomenon) occur at and after a certain viewing angle.On the other hand, when the viewing angle is gradually tilted from thedirection normal to the screen in the negative viewing direction (towardthe upper side of the screen), the contrast is abruptly reduced.

[0019] The above LCD device has another problem that as the displayscreen is larger the acceptable viewing angle becomes smaller. Forexample, when an observer views a large liquid crystal display screenfrom the front at a short distance, the observer may sometimes recognizethat the color displayed on the upper portion of the screen is differentfrom the color displayed on the lower portion thereof. This is because,as a display screen becomes larger, the apparent angle for viewing theentire screen becomes greater, causing the same phenomenon observed whenthe display screen is viewed in a tilted direction.

[0020] A method for overcoming the viewing angle dependence of the TNmode is proposed, where a phase plate (or a phase film) as an opticalelement (phase element) having optical anisotropy is provided betweenthe LCD element and a polarizing plate.

[0021] In this method, an elliptic polarized light beam to which alinear polarized light beam have been changed after passing throughliquid crystal molecules having refractive anisotropy is allowed to passthrough an optical phase plate having refractive index anisotropydisposed on at least one surface of a liquid crystal layer. Thiscompensates for a change in the phase difference between ordinary lightand extraordinary light generated depending on the viewing angle, andthus changes the elliptic polarized light beam back to the linearpolarized light beam. In this way, the viewing angle dependence isreduced.

[0022] Japanese Laid-Open Publication No. 5-313159, for example,proposes a method using an optical phase plate, in which the directionof one principal refractive index of an index ellipsoid of the opticalphase plate is made parallel to the normal of the surface of the opticalphase plate. Using this optical phase plate, however, only a limitedimprovement is obtained in the inversion phenomenon which occurs in thepositive viewing direction.

[0023] In order to overcome the above problem, Japanese Laid-OpenPublication No. 6-75116 proposes a method using an optical phase plate,in which the direction of a principal refractive index of an indexellipsoid is tilted from the normal of the surface of the optical phaseplate. In this method, two types of optical phase plates are proposed asfollows.

[0024] In one type of optical phase plate, the direction of the smallestprincipal refractive index among the three principal refractive indicesof the index ellipsoid of the optical phase plate is made parallel tothe surface of the optical phase plate. The direction of one of theremaining two principal refractive indices is tilted by an angle θ fromthe surface of the optical phase plate, while the direction of the otherprincipal refractive index is tilted by the angle θ from the normal ofthe surface of the optical phase plate, wherein θ is 20°≦θ≦70°.

[0025] In the other type of optical phase plate, the three principalrefractive indices na, nb, and nc of the index ellipsoid of the opticalphase plate have the relationship of na=no>nb. The direction of theprincipal refractive index nb is tilted clockwise or counterclockwisefrom the normal of the surface of the optical phase plate with respectto the direction of the principal refractive index na or nc which isparallel to the surface of the optical phase plate as an axis. At thesame time, the direction of the principal refractive index nc or na istilted clockwise or counterclockwise from the direction parallel to thesurface of the optical phase plate. In this way, the index ellipsoid ofthis optical phase plate is tilted.

[0026] In the former type, the respective optical phase plates may beuniaxial or biaxial. In the latter type, a single optical phase platemay be used. Alternatively, two optical phase plates may be used incombination so that the tilted directions of the respective principalrefractive indices nb form 90° therebetween.

[0027] By disposing at least one such optical phase plate between theLCD element and the polarizing plate, the change in contrast of adisplay image generated depending on the viewing angle, the coloringphenomenon, and the inversion phenomenon can be reduced to some extent.

[0028] Japanese Laid-Open Publication No. 8-101381 proposes a method forimproving the viewing angle characteristic for display color in an LCDdevice using the latter type of optical phase plate in the followingmanner: The wavelength dispersion of the refractive index anisotropy ofthe optical phase plate is made smaller than the wavelength dispersionof the refractive index anisotropy of the liquid crystal layer. JapaneseLaid-Open Publication No. 5-215912 discloses a method for improving theviewing angle characteristic in an LCD device using a conventionaloptical phase plate of which the index ellipsoid is not tilted in thesame manner, i.e., in the manner that the wavelength dispersion of therefractive index anisotropy is made smaller than that of the liquidcrystal layer.

[0029] The wavelength dispersion of an optical phase plate can beadjusted by changing the material for the optical phase plate or byadjusting the thickness of the optical phase plate.

[0030] In order to overcome the viewing angle dependence of LCD devicesof the TN and STN modes described above, Japanese Laid-Open PublicationNo. 57-1867835, for example, discloses an orientation dividing method,in which the portion of a liquid crystal layer corresponding to eachpixel region is divided into a plurality of domains so that a pluralityof viewing angle characteristics are obtained in each pixel region.Japanese Laid-Open Publication Nos. 7-234407 and 7-248497 disclose amethod in which a plurality of twist orientations of liquid crystalmolecules are provided in each pixel region.

[0031] However, when each pixel region is divided into two to form twoliquid crystal molecule orientation domains having different orientationstates within one pixel region, a problem arises in which completelydifferent viewing angle characteristics are exhibited between the upwardand downward directions (12 o'clock-6 o'clock directions) and the rightand left directions (3 o'clock-9 o'clock directions). For example, inthe upward and downward directions, when the viewing angle is dropped,the light transmittance during black display increases resulting ininsufficient contrast. In the right and left directions, while thecontrast is good, an inversion phenomenon occurs.

[0032] In the case where a plurality of twist orientations are providedin each pixel region or each pixel region is divided into a plurality ofdomains having different orientations, it is difficult to improve theviewing angle characteristic in the direction of 45° from an absorptionaxis or a transmission axis of a polarizing plate.

[0033] In order to overcome the above problem, Japanese Laid-OpenPublication Nos. 6-118406 and 6-194645 disclose techniques which combinethe above-described pixel region dividing method and the optical phaseplate.

[0034] More specifically, Japanese Laid-Open Publication No. 6-118406discloses an LCD device whose contrast is improved by inserting a film(an optical phase plate) having optical anisotropy between an LCDelement and a polarizing plate.

[0035] Japanese Laid-Open Publication No. 6-194645 discloses acompensation plate (optical phase plate) which is set so that arefractive index is substantially zero in the plane parallel to thesurface thereof and that a refractive index in a direction normal to thesurface thereof is smaller than the refractive index in the plane. Sucha compensation plate has a negative refractive index anisotropy, whichcan compensate for a positive refractive index anisotropy generated inthe LCD element when a voltage is applied. Thus, the viewing angledependence can be reduced.

[0036] Under the present circumstances, however, where LCD deviceshaving a wider angle of field and higher display quality are desired,the combination of the pixel region dividing method and a negativeuniaxial optical phase plate as described above are not sufficient forthe following reason. In the above techniques, the ratio of the areas oftwo liquid crystal molecule orientation domains in one pixel region(hereinafter, such a ratio is referred to as the division ratio) is 1:1(i.e., the areas are the same). Accordingly, although the viewing anglecharacteristic in the right and left directions can be improved by usinga uniaxial optical phase plate, the viewing angle characteristic in theupward and downward directions is not improved by only using a negativeuniaxial optical phase plate because using such an optical phase plateis simply equal to having_two liquid crystal molecule orientationdomains in which liquid crystal molecules are respectively oriented inthe 12 o'clock direction and the 6 o'clock direction in a conventionalTN mode LCD device.

[0037] Japanese Laid-Open Publication No. 10-3081 discloses a techniqueof combining a pixel region dividing method in which each pixel regionis divided at an unequal ratio (any ratio excluding 1:1) with an opticalphase plate of which the index ellipsoid is tilted as described above.In an LCD device disclosed in this publication, an LCD element and anoptical phase plate are arranged so that the tilt direction of the indexellipsoid of the optical phase plate is opposite to the pretiltdirection of liquid crystal molecules which are located in the vicinityof an alignment film in a larger liquid crystal molecule orientationdomain in each pixel region. By this arrangement, the angle of field inthe upward and downward directions, as well as in the right and leftdirections, can be widened.

[0038] However, the above prior art methods still have at least thefollowing problems. Under the present circumstances where LCD deviceshaving a wider angle of field and higher display quality are desired,further improvement on the viewing angle dependency is required. Usingonly an optical phase plate, as disclosed in the above mentionedJapanese Laid-Open Publication No. 6-75116, is not sufficient.

[0039] In the methods disclosed in Japanese Laid-Open Publication Nos.8-101381 and 5-215912, as mentioned above, it is not practical to use anoptical phase plate made of a material having appropriate wavelengthdispersion since this restricts the range of materials usable for theoptical phase plate. In the case of adjusting the thickness of theoptical phase plate, when the optical phase plate is thickened, thephase difference changes due to a change in the optical path length anda change in the index ellipsoid generated when the viewing angle isdropped. This frustrates the attempt of widening the angle of field andthus is not desirable in practice. Moreover, these methods do not reducethe coloring phenomenon of the display screen when the viewing angle isdropped downward. Therefore, these methods still have problems yet to beovercome.

[0040] As for the technique of combining the pixel region dividingmethod in which each pixel region is divided at an unequal ratio withthe optical phase plate of which the index ellipsoid is tilted asdescribed above, this technique alone is not considered sufficient tomeet the requirements of a wide angle of field, high display quality,and high color reproducibility.

[0041] In order to reduce the coloring phenomenon in the negativeviewing direction, the decrease in the contrast ratio, and the inversionphenomenon in the right and left directions in an LCD device using anoptical phase plate of which the index ellipsoid is tilted (hereinafter,such an optical phase plate is referred to as a tilted phase plate), thefollowing improvements are disclosed.

[0042] Japanese Laid-Open Publication No. 10-123503 discloses a methodin which the retardation d·Δn of a liquid crystal layer, i.e., theproduct of the refractive index anisotropy Δn of a liquid crystalmaterial and the cell thickness d, is set in the range between 300 nmand 550 nm, inclusive.

[0043] Japanese Laid-Open Publication No. 10-186532 discloses a methodin which a liquid crystal material having a small wavelength dispersionof the refractive index anisotropy Δn is used for an LCD device using atilted phase plate to reduce yellowish coloring in the right and leftdirections.

[0044] Japanese Laid-Open Publication No. 10-282485 discloses a methodfor adjusting the pretilt angle of liquid crystal molecules and thevoltage for white display, as well as adjusting the conditions of thewavelength dispersion nF of a tilted phase plate and the wavelengthdispersion nL of a liquid crystal material in an LCD using the tiltedphase plate in order to further widen the angle of field and reduceyellowish coloring in the right and left directions.

[0045] In order to improve yellowish coloring in the right and leftdirections in an LCD device using a tilted phase plate in which eachpixel region is divided at an unequal ratio, the following improvementsare disclosed.

[0046] Japanese Laid-Open Publication No. 10-246885 discloses a methodin which a liquid crystal material having a small wavelength dispersionof the refractive index anisotropy Δn is used.

[0047] Japanese Laid-Open Publication No. 9-233099 discloses a methodfor adjusting the conditions of the wavelength dispersion nF of a tiltedphase plate and the wavelength dispersion nL of a liquid crystalmaterial in an LCD using the tilted phase plate in which each pixel isdivided at an unequal ratio in order to reduce yellowish coloring in theright and left directions.

[0048] Japanese Laid-Open Publication No. 9-235181 discloses a methodfor adjusting the pretilt angle of liquid crystal molecules and thevoltage for white display in an LCD using a tilted phase plate in orderto further improve the display quality in the negative viewingdirection.

[0049] Despite the above improvements the following problem stillarises, in the case of disposing an optical phase plate (opticalanisotropy film) of which the index ellipsoid is tilted as describedabove between a polarizing plate and an LCD element, if the wavelengthdependence of the ordinary light refractive index and the extraordinarylight refractive index of a liquid crystal material does not matchnicely with the refractive index of the optical phase plate coloringbecomes significant when the viewing angle is dropped or during grayscale display; thus markedly deteriorating the state of display images.

[0050] An object of the present invention is to provide an LCD devicecapable of further reducing the change in contrast, the coloringphenomenon, the inversion phenomenon, and the like caused depending onthe viewing angle; and in particular, an LCD device capable ofeffectively reducing the coloring phenomenon on a liquid crystal screencaused depending on the viewing angle.

[0051] Another object of the present invention is to provide an LCDdevice in which a portion of a liquid crystal layer corresponding to onepixel region is divided into a plurality of liquid crystal moleculeorientation domains having different orientation states at an unequalratio, capable of widening the angle of field in the right and leftdirections as well as in the upward and downward directions andpreventing coloring from occurring when the viewing angle is dropped orduring gray scale display, thereby realizing high-quality image displaywith a wide angle of field.

SUMMARY OF THE INVENTION

[0052] The liquid crystal display device of this invention includes: aliquid crystal display element including a pair of substrates, a liquidcrystal layer interposed between the pair of substrates, and analignment film formed on a surface of at least one of the pair ofsubstrates facing the liquid crystal layer; a pair of polarizersdisposed on both surfaces of the liquid crystal element to sandwich theliquid crystal element; and at least one optical phase element disposedbetween at least one of the pair of polarizers and the liquid crystalelement, wherein three principal refractive indices na, nb, and na of anindex ellipsoid of the optical phase element have the relationship ofna=no>nb, a direction of the principal refractive index nb is tiltedclockwise or counterclockwise from the normal of a surface of theoptical phase element with respect to a direction of one of theprincipal refractive indices na and nc which is substantially parallelto the surface of the optical phase element as an axis, and a directionof the other principal refractive index nc or na is tilted clockwise orcounterclockwise from a direction substantially parallel to the surfaceof the optical phase element, and at least one of rates of variation ofan ordinary refractive index no and an extraordinary refractive index neof a liquid crystal material of the liquid crystal layer with respect toa wavelength is set in a range in which viewing angle dependent coloringdoes not occur on a screen.

[0053] Alternatively, the liquid crystal display device of thisinvention includes: a liquid crystal display element including a pair ofsubstrates, a liquid crystal layer interposed between the pair ofsubstrates, and an alignment film formed on a surface of at least one ofthe pair of substrates facing the liquid crystal layer; a pair ofpolarizers disposed on both surfaces of the liquid crystal element tosandwich the liquid crystal element; and at least one optical phaseelement disposed between at least one of the pair of polarizers and theliquid crystal element, wherein three principal refractive indices na,nb, and na of an index ellipsoid of the optical phase element have therelationship of na=nc>nb, a direction of the principal refractive indexnb is tilted clockwise or counterclockwise from the normal of a surfaceof the optical phase element with respect to a direction of one of theprincipal refractive indices na and nc which is substantially parallelto the surface of the optical phase element as an axis, and a directionof the other principal refractive index no or na is tilted clockwise orcounterclockwise from a direction substantially parallel to the surfaceof the optical phase element, and conditions of the combination of alength of a mean alkyl chain of a liquid crystal material of the liquidcrystal layer, a rate of variation of an ordinary refractive index no ofthe liquid crystal material with respect to a wavelength, and a rate ofvariation of an extraordinary refractive index ne of the liquid crystalmaterial with respect to a wavelength are set in a range in whichviewing angle dependent coloring does not occur on a screen.

[0054] In one embodiment of the invention, the liquid crystal displaydevice further includes a plurality of pixel regions for displaying,wherein at least one of the plurality of pixel regions is divided into afirst liquid crystal molecule orientation domain and a second liquidcrystal molecule orientation domain which have different orientationstates of liquid crystal molecules included in the liquid crystal layer,and the area of the first liquid crystal molecule orientation domain islarger than the area of the second liquid crystal molecule orientationdomain.

[0055] In another embodiment of the invention, the liquid crystaldisplay device further includes a plurality of pixel regions fordisplaying, wherein at least one of the plurality of pixel regions isdivided into a first liquid crystal molecule orientation domain and asecond liquid crystal molecule orientation domain which have differentorientation states of liquid crystal molecules included in the liquidcrystal layer, and the area of the first liquid crystal moleculeorientation domain is larger than the area of the second liquid crystalmolecule orientation domain.

[0056] In still another embodiment of the invention, the rate ofvariation among extraordinary light refractive indices ne(450), ne(550),and ne(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, and the rate of variation among ordinary light refractiveindices no(450), no(550), and no(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00.

[0057] In still another embodiment of the invention, the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, is set in a range of:

1.65≦(no(450)−no(550))/(no(550)−no(650))≦2.40.

[0058] In still another embodiment of the invention, the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, is set in a range of:

1.85≦(no(450)−no(550))/(no(550)−no(650))≦2.20.

[0059] In still another embodiment of the invention, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, is set in a range of:

1.70≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.30.

[0060] In still another embodiment of the invention, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, is set in a range of:

1.85≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.10.

[0061] In still another embodiment of the invention, the rate ofvariation among extraordinary light refractive indices ne(450), ne(550),and ne(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, and the rate of variation among ordinary light refractiveindices no(450), no(550), and no(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00.

[0062] In still another embodiment of the invention, the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, is set in a range of:

1.00≦(no(450)−no(550))/(no(550)−no(650))≦1.65.

[0063] In still another embodiment of the invention, the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, is set in a range of:

1.15≦(no(450)−no(550))/(no(550)−no(650))≦1.45.

[0064] In still another embodiment of the invention, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, is set in a range of:

1.20≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.70.

[0065] In still another embodiment of the invention, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, is set in a range of:

1.35≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.60.

[0066] In still another embodiment of the invention, the length m of themean alkyl chain (C_(m)H_(2m+1)—) of the liquid crystal material is setin a range of m<3.40, and the rate of variation among extraordinarylight refractive indices ne(450), ne(550), and ne(650) of the liquidcrystal material for light with wavelengths of 450 nm, 550 nm, and 650nm, respectively, and the rate of variation among ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in arange of:1.00 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ −0.422m + 2.55.

[0067] In still another embodiment of the invention, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) of the liquid crystal material for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, are set in a range of:1.00 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ −0.343m + 2.26.

[0068] In still another embodiment of the invention, the length m of themean alkyl chain (C_(m)H_(2m+1)—) of the liquid crystal material is setin a range of 3.40≦m≦3.90, and the rate of variation among extraordinarylight refractive indices ne(450), ne(550), and ne(650) of the liquidcrystal material for light with wavelengths of 450 nm, 550 nm, and 650nm, respectively, and the rate of variation among ordinary lightrefractive indices no(450), no(550), and nb(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in arange of:0.80 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.20.

[0069] In still another embodiment of the invention, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) of the liquid crystal material for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, are set in a range of:0.85 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.15.

[0070] In still another embodiment of the invention, the length m of themean alkyl chain (C_(m)H_(2m+1)—) of the liquid crystal material is setin a range of m>3.90, and the rate of variation among extraordinarylight refractive indices ne(450), ne(550), and ne(650) of the liquidcrystal material for light with wavelengths of 450 nm, 550 nm, and 650nm, respectively, and the rate of variation among ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in arange of:−0.422m + 2.55 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0071] In still another embodiment of the invention, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) of the liquid crystal material for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, are set in a range of:−0.343m + 2.26 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0072] In still another embodiment of the invention, a value ofrefractive index anisotropy Δn(550) of the liquid crystal material forlight with a wavelength of 550 nm is set in a range of:

0.060<Δn(550)<0.120.

[0073] In still another embodiment of the invention, a value ofrefractive index anisotropy Δn(550) of the liquid crystal material forlight with a wavelength of 550 nm is set in a range of:

0.060<Δn(550)<0.120.

[0074] In still another embodiment of the invention, the value of therefractive index anisotropy Δn(550) of the liquid crystal material forlight with a wavelength of 550 nm is set in a range of:

0.70<Δn(550)<0.095.

[0075] In still another embodiment of the invention, the value of therefractive index anisotropy Δn(550) of the liquid crystal material forlight with a wavelength of 550 nm is set in a range of:

0.070<Δn(550)<0.095.

[0076] In still another embodiment of the invention, a tilt angle of theindex ellipsoid of the optical phase element is set in a range between15° and 75° inclusive.

[0077] In still another embodiment of the invention, a tilt angle of theindex ellipsoid of the optical phase element is set in a range between15° and 75° inclusive.

[0078] In still another embodiment of the invention, the product of thedifference between the principal refractive indices na and nb of theoptical phase element and the thickness d of the optical phase element,i.e., (na−nb)×d is set in a range between 80 nm and 250 nm inclusive.

[0079] In still another embodiment of the invention, the product of thedifference between the principal refractive indices na and nb of theoptical phase element and the thickness d of the optical phase element,i.e., (na−nb)×d is set in a range between 80 nm and 250 nm inclusive.

[0080] In still another embodiment of the invention, the liquid crystaldisplay element and the optical phase element are arranged so that analignment direction of the alignment film is opposite to a tiltdirection of the principal refractive indices nb and nc of the opticalphase element in the first liquid crystal molecule orientation domain.

[0081] In still another embodiment of the invention, the liquid crystaldisplay element and the optical phase element are arranged so that analignment direction of the alignment film is opposite to a tiltdirection of the principal refractive indices nb and nc of the opticalphase element in the first liquid crystal molecule orientation domain.

[0082] In still another embodiment of the invention, the liquid crystaldisplay element and the optical phase element are arranged so that thealignment direction of the alignment film is the same as the tiltdirection of the principal refractive indices nb and nc of the opticalphase element in the second liquid crystal molecule orientation domain.

[0083] In still another embodiment of the invention, the liquid crystaldisplay element and the optical phase element are arranged so that thealignment direction of the alignment film is the same as the tiltdirection of the principal refractive indices nb and nc of the opticalphase element in the second liquid crystal molecule orientation domain.

[0084] In still another embodiment of the invention, an area ratio ofthe first liquid crystal molecule orientation domain to the secondliquid crystal molecule orientation domain in the at least one pixelregion is set in a range between 6:4 and 19:1 inclusive.

[0085] In still another embodiment of the invention, an area ratio ofthe first liquid crystal molecule orientation domain to the secondliquid crystal molecule orientation domain in the at least one pixelregion is set in a range between 6:4 and 19:1 inclusive.

[0086] In still another embodiment of the invention, liquid crystalmolecules in the liquid crystal layer are twisted about 90° between thepair of substrates.

[0087] In still another embodiment of the invention, liquid crystalmolecules in the liquid crystal layer are twisted about 90° between thepair of substrates.

[0088] Thus, the invention described herein makes possible theadvantages of (1) providing an LCD device capable of further reducingthe change in contrast, the coloring phenomenon, the inversionphenomenon, and the like caused depending on the viewing angle; and inparticular, an LCD device capable of effectively reducing the coloringphenomenon on a liquid crystal screen caused depending on the viewingangle, and (2) providing an LCD device in which a portion of a liquidcrystal layer corresponding to one pixel region is divided into aplurality of liquid crystal molecule orientation domains havingdifferent orientation states at an unequal ratio, capable of wideningthe angle of field in the right and left directions as well as in theupward and downward directions and preventing coloring from occurringwhen the viewing angle is dropped or during gray scale display, therebyrealizing high-quality image display with a wide angle of field.

[0089] These and other advantages of the present invention will becomeapparent to those skilled in the art upon reading and understanding thefollowing detailed description with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0090]FIG. 1 is a sectional view of an LCD device of an embodimentaccording to the present invention;

[0091]FIG. 2 is a view illustrating rubbing directions of an alignmentfilm and viewing angle directions in the LCD device of FIG. 1:

[0092]FIG. 3 is a perspective view illustrating the directions ofprincipal refractive indices of an optical phase plate in the LCD deviceof FIG. 1;

[0093]FIG. 4 is a perspective view illustrating optical arrangement ofan LCD element, polarizing plates, and the optical phase plates in theLCD device of FIG. 1;

[0094]FIG. 5 is a perspective view illustrating a measurement system formeasuring the viewing angle dependence of an LCD device;

[0095]FIGS. 6A to 6C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of Example 5 according to thepresent invention;

[0096]FIGS. 7A to 7C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of comparative examples;

[0097]FIGS. 8A to 8C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of Example 9 according to thepresent invention;

[0098]FIGS. 9A to 9C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of comparative examples;

[0099]FIG. 10 is a sectional view of an LCD device of an embodimentaccording to the present invention;

[0100]FIG. 11 is a view illustrating rubbing directions of an alignmentfilm and viewing angle directions in the LCD device of FIG. 10;

[0101]FIG. 12 is a perspective view illustrating optical arrangement ofan LCD element, polarizing plates, and the optical phase plates in theLCD device of FIG. 10;

[0102]FIGS. 13A to 13C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of Example 14 according to thepresent invention:

[0103]FIGS. 14A to 14C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of comparative examples;

[0104]FIGS. 15A to 15C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of Example 15 according to thepresent invention;

[0105]FIG. 16 is a graph showing the transmittance vs. applied voltagecharacteristics of LCD devices of comparative examples;

[0106]FIGS. 17A to 17C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of Example 19 according to thepresent invention;

[0107]FIGS. 18A to 18C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of comparative examples;

[0108]FIGS. 19A to 19C are graphs showing the transmittance vs. appliedvoltage characteristics of LCD devices of Example 20 according to thepresent invention;

[0109]FIG. 20 is a graph showing the transmittance vs. applied voltagecharacteristics of LCD devices of comparative examples; and

[0110]FIG. 21 is a schematic view illustrating the twisted orientationof liquid crystal molecules in a conventional TN type LCD element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0111] Hereinafter, the progress and function of the present inventionwill be described.

[0112] In the present invention, three principal refractive indices na,nb, and nc of an index ellipsoid of a phase element have therelationship of na=nc>nb. The direction of the principal refractiveindex nb is tilted clockwise or counterclockwise from the normal of thesurface of the phase element with respect to the direction of one of theprincipal refractive indices na and nc which is substantially parallelto the surface of the phase element as an axis. At the same time, thedirection of the other principal refractive index no or na is tiltedclockwise or counterclockwise from the direction substantially parallelto the surface of the phase element. In this way, the index ellipsoid ofthe phase element is tilted. When a linear polarized light beam passesthrough a liquid crystal layer having birefringence, generating ordinarylight and extraordinary light, it is changed to an elliptic polarizedlight beam due to the phase difference between the ordinary light andthe extraordinary light. By providing the phase element, the phasedifference between the ordinary light and the extraordinary light iscompensated.

[0113] However, with the above compensation function of the phaseelement alone, the goal of further reducing the visual dependence is notsatisfied.

[0114] According to the present invention, when the wavelengthdependence of the ordinary light refractive index no and theextraordinary light refractive index ne of a liquid crystal materialincluded in an LCD element does not match nicely with the wavelengthdependence of the refractive index of the phase element, coloringbecomes significant when the viewing angle is dropped or during grayscale display, markedly deteriorating the state of display images. Inparticular, it has been found that (1) the rate of variation of theordinary light reflective index no of the liquid crystal material withrespect to the wavelength and the rate of variation of the extraordinarylight reflective index ne of the liquid crystal material with respect tothe wavelength affect the coloring on, the liquid crystal displayscreen, and (2) the conditions of the combination of the mean alkylchain length of the liquid crystal material, the rate of variation ofthe ordinary light reflective index no of the liquid crystal materialwith respect to the wavelength, and the rate of variation of theextraordinary light reflective index ne of the liquid crystal materialwith respect to the wavelength affect the coloring on the liquid crystaldisplay screen. The present invention is based on the above findings.

[0115] In the LCD device according to the present invention, at leastone of the rates of variation of the ordinary light reflective index noand the extraordinary light reflective index ne of the liquid crystalmaterial with respect to the wavelength is set in the range in whichviewing angle dependent screen coloring does not occur. This furtherensures the prevention of the occurrence of screen coloring. Also, thechange in contrast and the inversion phenomenon can be further reduced,compared with the case of using only the compensation function of thephase element, as will be described later in embodiments of the presentinvention.

[0116] In the LCD device according to the present invention, theconditions of the combination of the mean alkyl chain length of theliquid crystal material, and the rates of variation of the ordinarylight reflective index no and the extraordinary light reflective indexne of the liquid crystal material with respect to the wavelength are setin a range in which viewing angle dependent screen coloring does notoccur. This further ensures the prevention of the occurrence of screencoloring. Also, the change in contrast and the inversion phenomenon canbe further reduced, compared with the case of using only thecompensation function of the phase element, as will be described laterin embodiments of the present invention.

[0117] As described above, by combining an LCD element in which aportion of a liquid crystal layer corresponding to one pixel region isdivided into a plurality of liquid crystal molecule orientation domainshaving different orientation states and different areas with a negativeuniaxial optical phase element of which the index ellipsoid is tilted,the angle of field can be widened in the upward and downward directions(12 o'clock-6 o'clock directions) as well as in the right and leftdirections (3 o'clock-9 o'clock directions).

[0118] In the LCD device with the above configuration, when the LCDelement and the optical phase element are arranged so that the directionin which liquid crystal molecules rise upon the application of a voltagein the largest liquid crystal molecule orientation domain in one pixelregion is opposite to the tilt direction of the index ellipsoid of theoptical phase element, the refractive index anisotropy of the liquidcrystal molecules which rise upon the application of a voltage in thelargest liquid crystal molecule orientation domain in the pixel regionis compensated by the negative uniaxial optical phase element. Thisimproves the contrast and reduces scale inversion, but causes a problemof destroying black scale. In order to overcome this problem, the LCDelement and the optical phase plate are also arranged so that thedirection in which liquid crystal molecules rise upon the application ofa voltage in the smallest liquid crystal molecule orientation domain inone pixel region is the same as the tilt direction of the indexellipsoid of the optical phase element. With this arrangement, since thesmallest liquid crystal molecule orientation domain has a viewing anglecharacteristic opposite to that of the largest liquid crystal moleculeorientation domain, the destruction of black scale in the largest liquidcrystal molecule orientation domain is reduced, and thus the angle offield in the upward and downward directions can be widened.

[0119] In the LCD device with the above configuration, however, if thewavelength dependence of the ordinary light refractive index no of theliquid crystal material and the wavelength dependence of theextraordinary light refractive index ne of the liquid crystal materialdo not match nicely with the wavelength dependence of the refractiveindex of the optical phase element, coloring on the display screenbecomes significant when the viewing angle is dropped or during grayscale display, markedly deteriorating the quality of display images.

[0120] In order to overcome the above problem, a design guideline forthe material for the liquid crystal layer has been established forrealizing a high quality LCD device having a wide angle of field inwhich the angle of field in the upward and downward directions as wellas the right and left directions is widened and coloring does not occurwhen the viewing angle is dropped or during gray scale display.

[0121] In the LCD device according to the present invention, a portionof the liquid crystal layer corresponding to at least one pixel regionis divided into a first liquid crystal molecule orientation domain and asecond liquid crystal molecule orientation domain so that the area ofthe first liquid crystal molecule orientation domain is larger than thearea of the second liquid crystal molecule orientation domain. Also, atleast one of the rates of variation of the ordinary light reflectiveindex no and the extraordinary light reflective index ne of the liquidcrystal material with respect to the wavelength is set in the range inwhich viewing angle dependent screen coloring does not occur.Alternatively, the portion of the liquid crystal layer corresponding toat least one pixel region is divided into a first liquid crystalmolecule orientation domain and a second liquid crystal moleculeorientation domain so that the area of the first liquid crystal moleculeorientation domain is larger than the area of the second liquid crystalmolecule orientation domain. Also, the conditions of the combination ofthe mean alkyl chain length of the liquid crystal material, and therates of variation of the ordinary light reflective index no and theextraordinary light reflective index ne of the liquid crystal materialwith respect to the wavelength are set in a range in which viewing angledependent screen coloring does not occur. This further prevents screencoloring from occurring, and also further reduces the change in contrastand the inversion phenomenon, compared with the case of using only thecompensation function of the phase element, as will be described laterin embodiments of the present invention.

[0122] As a result of further research, it has been found that, in someliquid crystal material for the liquid crystal layer of the LCD element,the range of the rate of variation of the refractive index with respectto the wavelength in which viewing angle dependent screen coloring doesnot occur is different depending on specific cases.

[0123] Based on the above findings, in the LCD device according to thepresent invention, at least one of the rates of variation of theordinary light refractive index no and the extraordinary lightrefractive index ne of the liquid crystal material, with respect to thewavelength, is set to be in a range in which viewing angle dependentscreen coloring does not occur, in the following two cases:

[0124] The extraordinary light refractive indices ne(450), ne(550), andne(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, and the ordinary light refractive indices no(450),no(550), and (650) for light with wavelengths of 450 nm, 550 nm, and 650nm, respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00, and((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00.

[0125] The rates of variation of the ordinary light refractive index noand the extraordinary light refractive index ne of the liquid crystalmaterial with respect to the wavelength are specifically set in thefollowing range.

[0126] (1) When the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and (650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00,

[0127] the rate of variation among the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, is set in the range of:

1.65≦(no(450)−no(550))/(no(550)−no(650))≦2.40.

[0128] Alternatively, the rate of variation among the extraordinarylight refractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, is set in therange of:

1.70≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.30.

[0129] By utilizing at least one of the above ranges, the resultantdisplay is sufficiently tolerable for use when viewed in any directionat a viewing angle of 50° required for a normal LCD device, althoughslight coloring is inevitable, as will be described later in Examples 1and 2. Otherwise, display images with a wide angle of field and highquality without coloring when the viewing angle is dropped or duringgray scale display are obtained, as will be described later in Examples10 and 11.

[0130] More preferably, the rate of variation is set in the followingrange:

1.85≦(no(450)−no(550))/(no(550)−no(650))≦2.20, or

1.85≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.10.

[0131] By utilizing at least one of the above ranges, the resultantdisplay has no coloring phenomenon at all when viewed in any directionat a wider viewing angle, 70°, as will be described later in Examples 1and 2. Otherwise, display images with a wide angle of field, highquality, and excellent reproducibility where coloring is furtherprevented are obtained, as will be described later in Examples 10 and11.

[0132] (2) When the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and (650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00,

[0133] the rate of variation among the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, is set in the range of:

1.00≦(no(450)−no(550))/(no(550)−no(650))≦1.65.

[0134] Alternatively, the rate of variation among the extraordinarylight refractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm is set in the range of:

1.20≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.70.

[0135] By utilizing at least one of the above ranges, the resultantdisplay is sufficiently tolerable when viewed in any direction at aviewing angle of 50° required for a normal LCD device, although slightcoloring is inevitable, as will be described later in Examples 3 and

[0136] 4. Otherwise, display images with a wide angle of field and highquality without coloring when the viewing angle is dropped or duringgray scale display are obtained, as, will be described later in Examples12 and 13.

[0137] More preferably, the rate of variation is set in the followingrange:

1.15≦(no(450)−no(550))/(no(550)−no(650))≦1.45, or

1.35≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.60.

[0138] By utilizing at least one of the above ranges, the resultantdisplay has no coloring phenomenon at all when viewed in any directionat a wider viewing angle, 70°, as will be described later in Examples 3and 4. Otherwise, display images with a wide angle of field, highquality, and excellent reproducibility where coloring is furtherprevented are obtained, as will be described later in Examples 12 and13.

[0139] The conditions of the combination of the mean alkyl chain lengthof the liquid crystal material and the rates of variation of theordinary light reflective index no and the extraordinary lightreflective index ne of the liquid crystal material with respect to thewavelength are specifically set in the following range.

[0140] (1) In the case where the length m of a mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is m<3.40, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range:1.00 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ −0.422m + 2.55.

[0141] By utilizing the above range, the resultant display issufficiently tolerable when viewed in any direction at a viewing angleof 50° required for a normal LCD device, although slight coloring isinevitable, as will be described later in Example 6. Otherwise, displayimages with a wide angle of field and high quality without coloring whenthe viewing angle is dropped or during gray scale display are obtained,as will be described later in Example 17.

[0142] More preferably, the rates of variation are set in the followingrange:1.00 ≤ (no(450) − no(550))/(no(550) − no(650))/(ne(450) − ne(550))/(ne(550) − ne(650)) ≤ −0.343m + 2.26.

[0143] By utilizing the above range, the resultant display has nocoloring phenomenon at all when viewed in any direction at a widerviewing angle, 70°, as will be described later in Example 6. Otherwise,display images with a wide angle of field, high quality, and excellentreproducibility without coloring are obtained, as will be describedlater in Example 17.

[0144] (2) In the case where the length of a mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is 3.40≦m≦3.90, the rateof variation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range:0.80 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.20.

[0145] By utilizing the above range, the resultant display issufficiently tolerable when viewed in any direction at a viewing angleof 50° required for a normal LCD device, although slight coloring isinevitable, as will be described later in Example 7. Otherwise, displayimages with a wide angle of field and high quality without coloring whenthe viewing angle is dropped or during gray scale display are obtained,as will be described later in Example 18.

[0146] More preferably, the rates of variation are set in the followingrange:0.85 < (no(450) − no(550))/(no(550) − no(650))/(ne(450) − ne(550))/(ne(550) − ne(650)) < 1.15.

[0147] By utilizing the above range, the resultant display has nocoloring phenomenon at all when viewed in any direction at a widerviewing angle, 70°, as will be described later in Example 7. Otherwise,display images with a wide angle of field, high quality, and excellentreproducibility without coloring are obtained, as will be describedlater in Example 18.

[0148] (3) In the case where the length of a mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is m>3.90, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range,−0.422m + 2.55 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0149] By utilizing the above range, the resultant display issufficiently tolerable when viewed in any direction at a viewing angleof 50° required for a normal LCD device, although slight coloring isinevitable, as will be described later in Example 8. Otherwise, displayimages with a wide angle of field and high quality without coloring whenthe viewing angle is dropped or during gray scale display are obtained,as will be described later in Example 16.

[0150] More preferably, the rates of variation are set in the followingrange:−0.343m + 2.26 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0151] By utilizing the above range, the resultant display has nocoloring phenomenon at all when viewed in any direction at a widerviewing angle, 70°, as will be described later in Example 8. Otherwise,display images with a wide angle of field, high quality, and excellentreproducibility without coloring are obtained, as will be describedlater in Example 16.

[0152] In the LCD device according to the present invention, therefractive index anisotropy An of the liquid crystal material for lighthaving a wavelength of 550 nm is preferably set in the range of

0.060<Δn(550)<0.120.

[0153] If the refractive index anisotropy Δn(550) of the liquid crystalmaterial for visible light having a wavelength of 550 nm is less than0.060 or more than 0.120, it has been confirmed that an inversionphenomenon and a reduction in the contrast ratio occur depending on theviewing angle direction. Such an inversion phenomenon will be describedlater in Examples 5, 9, 14, and 19. The phase difference depending onthe viewing angle can be eliminated by setting the refractive indexanisotropy Δn(550) of the liquid crystal material for light having awavelength of 550 nm in the range between 0.060 and 0.120, inclusive.Accordingly, the change in contrast and the inversion phenomenon in theright and left directions, as well as the coloring phenomenon occurringon the liquid crystal display screen depending on the viewing angle, canbe further reduced.

[0154] Furthermore, by setting the refractive index anisotropy Δn(550)of the liquid crystal material for light having a wavelength of 550 nmin the range of:

0.070≦Δn(550)≦0.095,

[0155] the phase difference of the LCD element depending on the viewingangle can be eliminated more effectively without fail, as will bedescribed later in Examples 5, 9, 14, and 19. Accordingly, it is ensuredthat the coloring phenomenon, the change in contrast, the inversionphenomenon in the right and left directions, which occur on the liquidcrystal display screen depending on the viewing angle, can be improved.

[0156] In the LCD device according to the present invention, the tiltangle of the index ellipsoid of the optical phase element is preferablyset in the range between 15° and 75° inclusive. By utilizing this range,it is ensured that the change in the phase difference between theordinary light and the extraordinary light caused depending on theviewing angle described above can be compensated by the optical phaseelement, as will be described later in Examples 5, 9, 14, and 19.

[0157] In the LCD device according to the present invention, the productof the difference between the principal refractive indices na and nb ofthe optical phase element and the thickness d of the optical phaseelement, i.e., (na−nb)×d, is preferably set in the range between 80 nmand 250 nm, inclusive. By utilizing this range, it is ensured that thechange in the phase difference between the ordinary light and theextraordinary light caused depending on the viewing angle, describedabove, can be compensated by the optical phase element, as will bedescribed later in Examples 5, 9, 14, and 19.

[0158] The LCD device according to the present invention is preferablyarranged so that the alignment direction of an alignment film for thelargest liquid crystal molecule orientation domain among a plurality ofliquid crystal molecule orientation domains having different liquidcrystal orientation states in one pixel region is opposite to the tiltdirection of the principal refractive indices nb and nc of the opticalphase element. By this arrangement, the direction in which liquidcrystal molecules rise upon the application of a voltage in the largestliquid crystal molecule orientation domain is opposite to the tiltdirection of the index ellipsoid of the optical phase plate.Accordingly, it is ensured that the optical anisotropy generated whenthe liquid crystal molecules rise can be compensated by the opticalphase element.

[0159] Moreover, the LCD device according to the present invention ispreferably arranged so that the alignment direction of an alignment filmfor the smallest liquid crystal molecule orientation domain in one pixelregion is the same as the tilt direction of the principal refractiveindices nb and nc of the optical phase element. The smallest liquidcrystal molecule orientation domain has the viewing angle characteristicopposite to that of the largest liquid crystal molecule orientationdomain. With the addition of this viewing angle characteristic,therefore, destruction of black scale in the largest liquid crystalmolecule orientation domain is reduced, and thus the angle of field inthe upward and downward directions can be widened.

[0160] When the portion of the liquid crystal layer corresponding to onepixel region is divided into two liquid crystal molecule orientationdomains, the division ratio of a first liquid crystal moleculeorientation domain to a second liquid crystal molecule orientationdomain is preferably in the range between 6:4 and 19:1, inclusive. Thissetting improves the contrast in the upward and downward directions,reduces black inversion, reduces the destruction of black scale, andthereby realizes a wider angle of field in the upward and downwarddirections, as will be described later in Examples 15 and 20.

[0161] The present invention is applicable to a TN mode LCD device inwhich liquid crystal molecules in a liquid crystal layer are twisted 90°between a pair of substrates. By applying the present invention, an LCDdevice with a wide angle of field, high display quality, and excellentreproducibility can be obtained.

[0162] Before the description of embodiments of the present invention,the term “pixel region” as used herein is defined as follows.

[0163] The LCD device according to the present invention includes aplurality of pixel regions for effecting display. One pixel regionrepresents a component of the LCD device constituting a pixel which is aminimum unit of display. Typically, in an active matrix LCD deviceincluding a plurality of active elements (e.g., TFTs) arranged in amatrix and a plurality of pixel electrodes switched on or off by therespective active elements, each pixel region includes each pixelelectrode, a portion of a counter electrode opposing the pixelelectrode, and a liquid crystal molecule orientation domain interposedtherebetween. In a single matrix LCD device including stripe-shapedelectrodes (scanning electrodes and signal electrodes) extending on apair of substrates to cross each other via a liquid crystal layertherebetween, each pixel region includes a crossing portion in which twostripe-shaped electrodes overlap and a liquid crystal moleculeorientation domain interposed therebetween.

[0164] In this specification, a viewing angle or direction which isdownward with respect to the Left-Right line (FIG. 2) is referred to as“positive”, and a viewing angle or direction which is upward withrespect to the Left-Right line is referred to as “negative”.

[0165] Further in this specification, orientation directions of theliquid crystal molecules are indicated using a hypothetical clock face.In detail, where the liquid crystal panel is located in the usualdirection for viewers, the top part of the liquid crystal panel isreferred to as “12 o'clock”, and the bottom part is referred to as “6o'clock”.

[0166] Hereinbelow, embodiments of the present invention will bedescried with reference to the accompanying drawings. In the drawings,components having similar functions are denoted by the same referencenumerals.

[0167] (Embodiment 1)

[0168]FIG. 1 is a sectional view of an LCD device of an embodimentaccording to the present invention. The LCD device of this embodimentincludes a liquid crystal cell 16 including an LCD element 1, a pair ofoptical phase plates 2 and 3, and a pair of polarizing plates 4 and 5,and a driving circuit 17.

[0169] The LCD element 1 includes a pair of electrode substrates 6 and 7and a liquid crystal layer 8 interposed therebetween. The electrodesubstrate 6 includes a base glass substrate (transparent substrate) 9,transparent electrodes 10 made of ITO (indium tin oxide) formed on thesurface of the glass substrate 9 facing the liquid crystal layer 8, andan alignment film 11 formed on the transparent electrodes 10. Theelectrode substrate 7 includes a base glass substrate (transparentsubstrate) 12, transparent electrodes 13 made of ITO (indium tin oxide)formed on the surface of the glass substrate 12 facing the liquidcrystal layer 8, and an alignment film 14 formed on the transparentelectrodes 13. A single alignment film may be formed on either one ofthe substrates.

[0170] The transparent electrodes 10 and 13 are connected to the drivingcircuit 17. In FIG. 1, only two pixel regions are shown forsimplification. It will be easily understood that the stripe-shapedtransparent electrodes 10 and 13, having a predetermined width, areformed on the glass substrates 9 and 12, respectively, over a displayportion of the LCD element 1 so that the transparent electrodes 10 onthe glass substrate 9 and the transparent electrodes 13 on the glasssubstrate 12 cross each other (perpendicular to each other, in thiscase) as is viewed at a position normal to the substrate surface.

[0171] The alignment films 11 and 14 are rubbed in advance so thatliquid crystal molecules in the liquid crystal layer 8 are twisted 90°between the alignment films. That is, as shown in FIG. 2, the alignmentfilms 11 and 14 are rubbed so that rubbing directions R₁ and R₂ of thealignment films 11 and 14, respectively, are perpendicular to eachother.

[0172] The electrode substrates 6 and 7 are bonded together with a sealresin 15, and a liquid crystal material is sealed in a space enclosed bythe electrode substrates 6 and 7 and the seal resin 15 to form theliquid crystal layer 8. As will be described below in detail, in theliquid crystal layer 8, the rates of variation of the ordinary lightrefractive index no and the extraordinary light refractive index ne ofthe liquid crystal material with respect to the wavelength are preset tobe in a predetermined range so that- optimal characteristics can beobtained in combination with the optical phase difference compensatingfunction of the optical phase plates 2 and 3.

[0173] The optical phase plates 2 and 3 are disposed between the LCDelement 1 and the polarizing plates 4 and 5, respectively, located onboth surfaces of the LCD element 1. Each of the optical phase plates 2and 3 includes a support made of a transparent organic polymer and adiscotic liquid crystal material crosslinked to the support in a tiltedor hybrid orientation, so that an index ellipsoid thereof is tilted aswill be described later.

[0174] The support of the optical phase plates 2 and 3 is preferablymade of triacetyl cellulose (TAC) which is generally used for apolarizing plate. Using this material, a reliable optical phase plate isobtained. Other materials suitable for the support include transparentand colorless organic polymer films with excellent environmentresistance and chemical resistance, such as polycarbonate (PC) andpolyethylene terephthalate (PET) films.

[0175] As shown in FIG. 3, each of the optical phase plates 2 and 3 hasprincipal refractive indices na, nb, and nc representing three differentdirections. The three principal refractive indices na, nb, and nc havethe relationship of na=nc>nb. In this case, since the optical phaseplate 2, 3 is uniaxial, having a single optical axis, the refractiveindex anisotropy is negative.

[0176] The direction of the principal refractive index na is identicalto the y-axis in the rectangular coordinate system xyz, which isparallel to the surface of the optical phase plates 2 and 3 (parallel tothe screen). The direction of the principal refractive index nb istilted by an angle of θ in the direction of an arrow A from the z-axiswhich is normal to the surface of the optical phase plates 2 and 3(perpendicular to the screen) with respect to the direction of theprincipal refractive index na as an axis. The direction of the principalrefractive index no is tilted by the angle of θ in the direction of anarrow B from the x-axis which is parallel to the surface of the opticalphase plates 2 and 3 (parallel to the screen) with respect to thedirection of the principal refractive index na as an axis. The tiltangle θ of the index ellipsoid is preferably in the range of 15°≦θ≦75°.By utilizing this range, the optical phase plates 2 and 3 are ensured toperform the optical phase difference compensating function irrespectiveof whether the tilt direction of the index ellipsoid is clockwise orcounterclockwise. In FIG. 3, the reference numeral D denotes thedirection obtained by projecting, on the surface of the optical phaseplates 2 and 3, the direction of the principal refractive index nb whichis the direction providing anisotropy to the optical phase plates 2 and3.

[0177] A first retardation value of the optical phase plates 2 and 3 isexpressed by the product of the difference (refractive index anisotropyΔn) between the principal refractive indices na and nc and the thicknessd of the optical phase plate ((nc−na)×d). Since na=nc, the firstretardation value is substantially 0 nm. A second retardation value ofthe optical phase plates 2 and 3 are expressed by the product of thedifference (refractive index anisotropy Δn) between the principalrefractive indices na and nb and the thickness d of the optical phaseplate ((na−nb)×d). The second retardation value is preferably set in therange between 80 nm and 250 nm inclusive. Setting the value in thisrange ensures that the optical phase plates 2 and 3 provide the opticalphase plate compensating function.

[0178] In an optical anisotropic material such as a liquid crystalmaterial and an optical phase plate (film), the anisotropy of theprincipal refractive indices na, nb, and nc in the three-dimensionaldirections is represented by the index ellipsoid. The value of therefractive index anisotropy Δn of the index ellipsoid varies dependingon the direction in which the refractive index anisotropic material isobserved.

[0179] In the LCD device of this embodiment, the LCD element 1, theoptical phase plates 2 and 3, and the polarizing plates 4 and 5 arearranged as shown in FIG. 4.

[0180] The polarizing plate 4 is arranged so that an absorption axis AX₁thereof is parallel to the rubbing direction R₁ (FIG. 2) of thealignment film 11 described above, while the polarizing plate 5 isarranged so that an absorption axis AX₂ thereof is parallel to therubbing direction R₂ (FIG. 2) of the alignment film 14. Since therubbing directions R₁ and R₂ are orthogonal to each other, theabsorption axis AX₁ and AX₂ are also orthogonal to each other.

[0181] The optical phase plate 2 is arranged so that a direction D₁(corresponding to the direction D described with reference to FIG. 3) isparallel to the rubbing direction R₁, while the optical phase plate 3 isarranged so that a direction D₂ (corresponding to the direction Ddescribed with reference to FIG. 3) is parallel to the rubbing directionR₂.

[0182] With the above arrangement of the LCD element 1, the opticalphase plates 2 and 3, and the polarizing plates 4 and 5, the resultantLCD device provides a so-called normally-white mode in which light istransmitted when no ON voltage is applied to the liquid crystal layer 8to effect white display.

[0183] Only one of the optical phase plates 2 and 3 may be disposed oneither one surface of the LCD element 1. Alternatively, both the opticalphase plates 2 and 3 may be disposed on either one surface of the LCDelement 1 in the manner of one on top on the other. It is also possibleto use three or more optical phase plates.

[0184] Hereinbelow, the liquid crystal layer 8 will be described. Asdescribed above, in order to obtain optimal characteristics incombination with the optical phase difference compensating function ofthe optical phase plates 2 and 3, the rates of variation of the ordinarylight refractive index no and the extraordinary light refractive indexne of the liquid crystal material with respect to the wavelength arepreset to be in a predetermined range in which viewing angle dependentcoloring does not occur on the display screen.

[0185] More specifically, the rates of variation of the ordinary lightrefractive index no and the extraordinary light refractive index ne ofthe liquid crystal material with respect to the wavelength are set so asto satisfy at least one of setting ranges (a) and (b) in each of thefollowing conditions (1) and (2).

[0186] (1) When the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00,

[0187] (a) The rate of variation among the ordinary light refractiveindices no(450), no(550), and no(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, is set in the range of:

1.65≦(no(450)−no(550))/(no(550)−no(650))≦2.40.

[0188] More preferably, the rate of variation is set in the followingrange:

1.85≦(no(450)−no(550))/(no(550)−no(650))≦2.20.

[0189] (b) The rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, is set in therange of:

1.70≦(ne(450)−ne(550))/(ne(550)−ne(650))≦

[0190] 2.30.

[0191] More preferably, the rate of variation is set in the followingrange:

1.85≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.10.

[0192] (2) When the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00,

[0193] (a) The rate of variation among the ordinary light refractiveindices no(450), no(550), and no(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, is set in the range of:

1.00≦(no(450)−no(550))/(no(550)−no(650))≦1.65.

[0194] More preferably, the rate of variation is set in the followingrange:

1.15≦(no(450)−no(550))/(no(550)−no(650))≦1.45.

[0195] (b) The rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, is set in therange of:

1.20≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.70.

[0196] More preferably, the rate of variation is set in the followingrange:

1.35≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.60.

[0197] By utilizing the above ranges, in the LCD device of thisembodiment, a change in the optical phase difference between theordinary light and the extraordinary light which occurs in the LCDelement 1 depending on the viewing angle can be compensated by theoptical phase plates 2 and 3. Moreover, viewing angle dependent coloringoccurring on the liquid crystal display screen can be especiallyeffectively compensated by the liquid crystal material in the liquidcrystal layer 8. As a result, since viewing angle dependent coloring onthe display screen is effectively reduced and, at the same time, thecontrast change and the inversion phenomenon are reduced, high-qualityimages can be obtained.

[0198] Hereinbelow, the LCD device of this embodiment will be describedby way of specific examples.

EXAMPLE 1

[0199] In Example 1, in the LCD device shown in FIG. 1, a liquid crystalmaterial for the liquid crystal layer 8 was set so that: theextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, are in the range of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00; and

[0200] the rate of variation among the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm is in the range of:

1.65≦(no(450)−no(550))/(no(550)−no(650))≦2.40.

[0201] Such a liquid crystal material was prepared by blending materialsrepresented by structural formula (1) below:

[0202] The cell thickness of the liquid crystal cell 16 (the thicknessof the liquid crystal layer 8) was set at about 5 μm. Five samples ofsuch LCD devices as shown in Table 1 below (samples #11a to #15a) wereproduced.

[0203] In these samples, the optical phase plates 2 and 3 were formed inthe following manner. A discotic liquid crystal material was applied toa transparent support (made of triacetyl cellulose (TAC), for example).The discotic liquid crystal material was crosslinked in a tiltedorientation so that the first retardation value (nc−na)×d is 0 while thesecond retardation value (na−nb)×d is 100 nm, and that the tilt angle θof a tilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis direction in the xyz coordinatesystem and the direction of the principal refractive index no is tiltedby about 20° in the direction of the arrow B from the x-axis.

[0204] For comparison, two comparative samples of LCD devices as shownin Table 1 below (comparative samples #100a and #101a) were produced inthe same manner as that used in the above samples of this example exceptthat liquid crystal materials having a rate of variation((no(450)−no(550)/(no(550)−no(650)) of 1.55 and 2.50 were used for theliquid crystal layer 8 of the LCD device shown in FIG. 1.

[0205] Table 1 shows the results of visual inspections performed underwhite light for samples #11a to #15a and comparative samples #100aand#101a. In Table 1, as well as Tables 2 to 4 for Examples 2 to 4, tobe described later, the mark ◯ represents “no coloring”, Δ represents“tolerable coloring”, and χ represents “intolerable coloring”. TABLE 1Sample #100a #11a #12a #13a #14a #15a #101a Viewing angle ((no(450) −no(550))/((no(550) − no(650)) (θ) 1.55 1.65 1.85 2.05 2.20 2.40 2.50 50°x ∘ ∘ ∘ ∘ ∘ x 60° x Δ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0206] It is found from Table 1 that in samples #12a to #14a no coloringwas observed in any direction at a viewing angle of 70°, providing goodimage quality. This indicates that especially excellent characteristicsare provided in the range of the rate of variation of:

1.85≦(no(450)−no(550))/(no(550)−no(650))≦2.20.

[0207] It is also found from Table 1 that in samples #11a and #15a nocoloring was observed at a viewing angle of 50°, providing good imagequality. At a viewing angle of 60°, although slight coloring wasobserved when viewed in the right and left directions, it was in such alevel that was tolerable for use.

[0208] As for comparative samples #100a and #101a, yellow to orangecoloring intolerable for use was observed even at a viewing angle of 50°when viewed in the right and left directions.

[0209] The same results were obtained for samples of LCD devicesproduced in the same manner as that in samples #11a to #15a andcomparative samples #100a and #101a, except that the optical phaseplates 2 and 3 were made of a discotic liquid crystal material appliedto a transparent support and crosslinked in a hybrid orientation.

EXAMPLE 2

[0210] In Example 2, in the LCD device shown in FIG. 1, the liquidcrystal material for the liquid crystal layer 8 was set so that: theextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengthS of 450 nm, 550nm, and 650 nm, respectively, are in the range of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00; and

[0211] the rate of variation among the extraordinary light refractiveindices ne(450), ne(550), and ne(650) for light with wavelengths of 450nm, 550 nm, and 650 nm is in the range of:

1.70≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.30.

[0212] Such a liquid crystal material was prepared by blending thematerials shown in Example 1.

[0213] The cell thickness of the liquid crystal cell 16 was set at 5 μm.Five samples of such LCD devices as shown in Table 2 below (samples #21ato #25a) were produced.

[0214] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (no−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis direction in the xyz coordinatesystem and the direction of the principal refractive index no is tiltedby about 20° in the direction of the arrow B from the x-axis.

[0215] For comparison, two comparative samples of LCD devices as shownin Table 2 below (comparative samples #200a and #201a) were produced inthe same manner as that in the above samples of this example, exceptthat liquid crystal materials having a rate of variation((ne(450)−ne(550)/(ne(550)−ne(650)) of 1.60 and 2.40 were used for theliquid crystal layer 8 of the LCD device shown in FIG. 1.

[0216] Table 2 shows the results of visual inspections performed underwhite light for samples #21a to #25a and comparative samples #200a and#201a. TABLE 2 Sample #200a #21a #22a #23a #24a #25a #201a Viewing angle(ne(450) − ne(550))/(ne(550) − ne(650)) (θ) 1.60 1.70 1.85 1.90 2.102.30 2.40 50° x ∘ ∘ ∘ ∘ ∘ x 60° x Δ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0217] It is found from Table 2 that in samples #22a to #24a no coloringwas observed in any direction at a viewing angle of 70°, providing goodimage quality. This indicates that especially excellent characteristicsare provided in the range of the rate of variation of:

1.85≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.10.

[0218] It is also found from Table 2 that in samples #21a and #25a nocoloring was observed at a viewing angle of 50°, providing good imagequality. At a viewing angle of 60°, although slight coloring wasobserved when viewed in the right and left directions, it was in such alevel that was tolerable for use.

[0219] As for comparative samples #200a and #201a, yellow to orangecoloring intolerable for use was observed even at a viewing angle of 50°when viewed in the right and left directions.

[0220] The same results were obtained for samples of LCD devicesproduced in the same manner as that in samples #21a to #25a andcomparative samples #200a and #201a, except that the optical phaseplates 2 and 3 were made of a discotic liquid crystal material appliedto a transparent support and crosslinked in a hybrid orientation.

EXAMPLE 3

[0221] In Example 3, in the LCD device shown in FIG. 1, the liquidcrystal material for the liquid crystal layer 8 was set so that: theextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, are in the range of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00; and

[0222] the rate of variation among the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm is in the range of

1.00≦(no(450)−no(550))/(no(550)−no(650))≦1.65.

[0223] Such a liquid crystal material was prepared by blending thematerials shown in Example 1.

[0224] The cell thickness of the liquid crystal cell 16 was set at 5 μm.Five samples of such LCD devices as shown in Table 3 below (samples #31ato #35a) were produced.

[0225] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value(na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis direction in the xyz coordinatesystem and the direction of the principal refractive index no is tiltedby about 20° in the direction of the arrow B from the x-axis.

[0226] For comparison, two comparative samples of LCD devices as shownin Table 3 below (comparative samples #300a and #301a) were produced inthe same manner as that in the above samples of this example, exceptthat liquid crystal materials having a rate of variation((no(450)−no(550)/(no(550)−no(650)) of 0.90 and 1.75 were used for theliquid crystal layer 8 of the LCD device shown in FIG. 1.

[0227] Table 3 shows the results of visual inspections performed underwhite light for samples #31a to #35a and comparative samples #300a and#301a. TABLE 3 Sample #300a #31a #32a #33a #34a #35a #301a Viewing angle(no(450) − no(550))/(no(550) − no(650)) (θ) 0.90 1.00 1.15 1.30 1.451.65 1.75 50° x ∘ ∘ ∘ ∘ ∘ x 60° x Δ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0228] It is found from Table 3 that in samples #32a to #34a no coloringwas observed even when the viewing angle was dropped to 70°, providinggood image quality. This indicates that especially excellentcharacteristics are provided in the range of the rate of variation of:

1.15≦(no(450)−no(550))/(no(550)−no(650))≦1.45.

[0229] It is also found from Table 3 that in samples #31a and #35a nocoloring was observed at a viewing angle of 50°, providing good imagequality. At a viewing angle of 60°, although slight coloring wasobserved when viewed in the right and left directions, it was in such alevel that was tolerable for use.

[0230] As for comparative samples #300a and #301a, yellow to orangecoloring intolerable for use was observed even at a viewing angle of 50°when viewed in the right and left directions.

[0231] The same results were obtained for samples of LCD devicesproduced in the same manner as that in samples #31a to #35a andcomparative samples #300a and #301a, except that the optical phaseplates 2 and 3 were made of a discotic liquid crystal material appliedto a transparent support and crosslinked in a hybrid orientation.

EXAMPLE 4

[0232] In Example 4, in the LCD device shown in FIG. 1, the liquidcrystal material for the liquid crystal layer 8 was set so that: theextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, are in the range of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00; and

[0233] the rate of variation among the extraordinary light refractiveindices ne(450), ne(550), and ne(650) for light with wavelengths of 450nm, 550 nm, and 650 nm is in the range of:

1.20≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.70.

[0234] Such a liquid crystal material was prepared by blending thematerials shown in Example 1.

[0235] The cell thickness of the liquid crystal cell 16 was set at 5 μm.Five samples of such LCD devices as shown in Table 4 below (samples #41ato #45a) were produced.

[0236] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis direction in the xyz coordinatesystem and the direction of the principal refractive index no is tiltedby about 20° in the direction of the arrow B from the x-axis.

[0237] For comparison, two comparative samples of LCD devices as shownin Table 4 below (comparative samples #400a and #401a) were produced inthe same manner as that in the above samples of this example, exceptthat liquid crystal materials having a rate of variation((ne(450)−ne(550)/(ne(550)−ne(650)) of 1.10 and 1.80 were used for theliquid crystal layer 8 of the LCD device shown in FIG. 1.

[0238] Table 4 shows the results of visual inspections performed underwhite light for samples #41a to #45a and comparative samples #400a and#401a. TABLE 4 Sample #400a #41a #42a #43a #44a #45a #401a Viewing angle(ne(450) − ne(550))/(ne(550) − ne(650)) (θ) 1.10 1.20 1.35 1.50 1.601.70 1.80 50° x ∘ ∘ ∘ ∘ ∘ x 60° x Δ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0239] It is found from Table 4 that in samples #42a to #44a no coloringwas observed when the viewing angle was dropped to 70°, providing goodimage quality. This indicates that especially excellent characteristicsare provided in the range of the rate of variation of:

1.35≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.60.

[0240] It is also found from Table 4 that in samples #41a and #45a nocoloring was observed at a viewing angle of 50°, providing good imagequality. At a viewing angle of 60°, although slight coloring wasobserved when viewed in the right and left directions, it was in such alevel that was tolerable for use.

[0241] As for comparative samples #400a and #401a, yellow to orangecoloring intolerable for use was observed even at a viewing angle of 50°when viewed in the right and left directions.

[0242] The same results were obtained for samples of LCD devicesproduced in the same manner as that in samples #41a to #45a andcomparative samples #400a and #401a, except that the optical phaseplates 2 and 3 were made of a discotic liquid crystal material appliedto a transparent support and crosslinked in a hybrid orientation.

EXAMPLE 5

[0243] In Example 5, three samples (samples #51a to #53a) of the LCDdevice shown in FIG. 1 were produced using liquid crystal materials ofwhich the values of the refractive index anisotropy Δn(550) for lightwith a wavelength of 550 nm were set at 0.070, 0.080, and 0.095,respectively. The cell thickness of the liquid crystal cell 16 of thesesamples was 5 μm. The rates of variation of the ordinary lightrefractive index no and the extraordinary light refractive index ne ofeach sample are shown in Table 5 below. TABLE 5 Sample #51a #52a #53a#501a #502a Rate of variation of n_(o) 1.15 2.05 2.20 1.85 2.05 Rate ofvariation of n_(e) 1.35 1.90 2.10 1.85 1.90

[0244] As the optical phase plates 2 and 3, those including a discoticliquid crystal material in a tilted orientation as in Example 1 wereused.

[0245] For comparison, two comparative samples of LCD devices as shownin Table 5 above (comparative samples #501a and #502a) were produced inthe same manner as that used in the above samples of this example exceptthat liquid crystal materials of which the values of the refractiveindex anisotropy Δn for light with a wavelength of 550 nm were set at0.060 and 0.120, respectively.

[0246] The LCD devices of samples #51a to #53a and comparative samples#501a and #502a were measured for the viewing angle dependence using ameasurement system as shown in FIG. 5 which includes a light-receivingelement 18, an amplifier 19, and a recording device 20.

[0247] Referring to FIG. 5, the liquid crystal cell 16 of the LCD deviceto be measured is placed in the measurement system so that a surface 16a of the liquid crystal cell 16 is in the reference plane x-y of therectangular coordinate system xyz.

[0248] The light-receiving element 18 can receive light at a constantsolid light-receiving angle and is positioned at a predetermineddistance from the origin of the coordinate system in a direction of anangle φ (viewing angle) from the z-axis which is normal to the surface16 a of the liquid crystal cell 16.

[0249] In the measurement, the surface opposite to the surface 16 a ofthe liquid crystal cell 16 placed in the measurement system isirradiated with monochrome light with a wavelength of 550 nm. Part ofthe monochrome light which has passed through the liquid crystal cell 16is incident on the light-receiving element 18. The output of thelight-receiving element 18 is amplified to a predetermined level by theamplifier 19, and then recorded by the recording device 20 including awaveform memory, a recorder, and the like.

[0250] The LCD devices of samples #51a to #53a and comparative samples#501a and #502a were placed in the above measurement system, to measurethe relationship between the voltage applied to the LCD devices and theoutput level of the light-receiving element 18 when the light-receivingelement 18 was fixed at a constant angle φ.

[0251] It was assumed that the x-axis direction is toward the lower sideof the screen and the y-axis direction is toward the left side thereof.The measurement was performed by changing the position of thelight-receiving element 18 among positions at an angle φ of 50° in theupward direction, the right direction, and the left direction.

[0252] The measurement results of samples #51a to #53a are shown inFIGS. 6A to 6C, while those of comparative samples #501a and #502a areshown in FIGS. 7A to 7C. FIGS. 6A to 6C and 7A to 7C are graphs of thelight transmittance of the LCD devices with respect to the voltageapplied thereto (transmittance vs. applied voltage characteristics):FIGS. 6A and 7A show the results obtained when measured from the upperside as is viewed from FIG. 5; FIGS. 6B and 7B show the results obtainedwhen measured from the right side as is viewed from FIG. 5: and FIGS. 6Cand 7C show the results obtained when measured from the left side as isviewed from FIG. 5.

[0253] Referring to FIGS. 6A to 6C, curves L1 a, L4 a, and L7 a (theone-dot dash lines) represent sample #51a which uses a liquid crystalmaterial with Δn(550) of 0.070 for the liquid crystal layer 8, curves L2a, L5 a, and L8 a (the solid lines) represent sample #52a which uses aliquid crystal material with Δn(550) of 0.080 for the liquid crystallayer 8, and curves L3 a, L6 a, and L9 a (the dashed lines) representsample #53a which uses a liquid crystal material with Δn(550) of 0.095for the liquid crystal layer 8. Referring to FIGS. 7A to 7C, curves L10a, L12 a, and L14 a (the solid lines) represent comparative sample #501awhich uses a liquid crystal material with Δn(550) of 0.060 for theliquid crystal layer 8, and curves L11 a, L13 a, and L15 a (the dashedlines) represent sample #502a which uses a liquid crystal material withΔn(550) of 0.120 for the liquid crystal layer 8.

[0254] As for the transmittance vs. applied voltage characteristicsmeasured from the upper side, as shown by curves L1 a to L3 a in FIG.6A, it was confirmed that in samples #51a to #53a as the voltageincreased the transmittance sufficiently decreased. On the contrary, incomparative sample #502a, as shown by curve L11 a in FIG. 7A, as thevoltage increased the transmittance did not sufficiently decrease. Incomparative sample #501a, as shown by curve L10 a in FIG. 7A, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0255] Likewise, as for the transmittance vs. applied voltagecharacteristics measured from the right side, as shown by curves L4 a toL6 a in FIG. 6B, it was confirmed that in samples #51a to #53a as thevoltage increased the transmittance decreased to nearly zero. Incomparative sample #501a, as shown by curve L12 a in FIG. 7B, as thevoltage increased the transmittance decreased to nearly zero. However,in comparative sample #502a, as shown by curve L13 a in FIG. 7B, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0256] Likewise, as for the transmittance vs. applied voltagecharacteristics measured from the left side, as shown by curves L7 a toL9 a in FIG. 6C, it was confirmed that in samples #51a to #53a as thevoltage increased the transmittance decreased to nearly zero. Incomparative sample #501a, as shown by curve L14 a in FIG. 7C, as thevoltage increased the transmittance decreased to nearly zero. However,in comparative sample #502a, as shown by curve L15 a in FIG. 7C, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0257] Visual inspection was performed for samples #51a to #53a andcomparative samples #501a and #502a under white light. As a result, forsamples #51a to #53a of this example and comparative sample #501a, nocoloring was observed in any direction at a viewing angle of 50° orless, providing good image quality.

[0258] For comparative sample #502a, however, yellow to orange coloringwas observed when viewed from the right and left sides at a viewingangle of 50°.

[0259] From the above results, the following are recognized: As shown inFIGS. 6A to 6C, as for the samples of the LCD device of this example(samples #51a to #53a) using, for the liquid crystal layer 8, a liquidcrystal material of which the values of the refractive index anisotropyΔn(550) for light with a wavelength of 550 nm were set at 0.070, 0.080,and 0.095, when the voltage was increasingly applied, the transmittancesufficiently decreased, preventing an inversion phenomenon fromoccurring and thus widening the angle of field. Moreover, since nocoloring phenomenon was observed, the display quality of the LCD devicesignificantly improved.

[0260] On the contrary, as shown in FIGS. 7A to 7C, as for thecomparative samples of the LCD devices (comparative samples #501a and#502a) using liquid crystal materials of which the values of therefractive index anisotropy Δn(550) for 550 nm light were set at 0.060and 0.120, the viewing angle dependence was not sufficiently improved.

[0261] The same results as those described above were also obtained forsamples of LCD devices produced in the same manner as that used insamples #51a to #53a and comparative samples #501a and #502a, exceptthat the optical phase plates 2 and 3 were made of a discotic liquidcrystal material applied to a transparent support and crosslinked in ahybrid orientation.

[0262] The dependence of the transmittance vs. applied voltagecharacteristics on the tilt angle θ was examined by changing the tiltangle θ of the index ellipsoid of the optical phase plate 2 or 3. As aresult, essentially the same results as those described above wereobtained, irrespective of the orientation state of the discotic liquidcrystal material used for the optical phase plate 2 or 3, if the angle θis in the range of 15°≦θ75°. If the angle θ is less than 15° or exceeds75°, it was confirmed that the angle of field is not widened in thenegative viewing direction.

[0263] The dependence of the transmittance vs. applied voltagecharacteristics on the second retardation value (na−nb)×d was examinedby changing the second retardation value. As a result, essentially thesame results as those described above were obtained, irrespective of theorientation state of the discotic liquid crystal material used for theoptical phase plates 2 and 3, if the second retardation value is in therange between 80 nm and 250 nm, inclusive. If the second retardationvalue is less than 80 nm or exceeds 250 nm, it was confirmed that theangle of field is not widened in the lateral (right and left)directions.

[0264] Additional three samples of the LCD device shown in FIG. 1(samples #54a to #56a) were produced based on the results of the visualinspection of comparative samples #501a and #502a in the same manner asthat used for samples #51a to #53a except that liquid crystal materialsof which the values of the refractive index anisotropy for 550 nm lightwere set at 0.065, 0.100, and 0.115 were used for the liquid crystallayer 8.

[0265] Samples #54a to #56a of the LCD devices were placed in themeasurement system shown in FIG. 5. The relationship between the voltageapplied to the respective LCD devices and the output level of thelight-receiving element 18 obtained when the light-receiving element 18was fixed at a constant angle φ was measured, and the visual inspectionwas performed under white light.

[0266] The results of the above measurement and inspection are asfollows. In samples #55a and #56a of this example in which the values ofthe refractive index anisotropy Δn(550) were set at 0.100 and 0.115, aslight increase in transmittance was observed as the voltage wasincreased when measured from the right and left sides at an angle φ of50°. However, with no inversion phenomenon observed in the visualinspection, such a level of increase in transmittance was tolerable foruse. When measured from the upper side, samples #55a and #56a had noproblem.

[0267] In sample #54a in which the value of the refractive indexanisotropy Δn(550) was set at 0.065, as the voltage increased, thetransmittance initially decreased and then increased again, causing aninversion phenomenon, when measured from the upper side, as incomparative sample #501a described above. However, the degree of theincrease in transmittance was small enough to be tolerable for use,compared with the case of comparative sample #501a (L10 a) shown in FIG.7A. When measured from the right and left sides, sample #54a had noproblem.

[0268] In the visual inspection, slight yellow to orange coloring wasobserved in samples #55a and #56a, although it was too slight to raise aproblem. For sample #54a, slight blue coloring was observed, although itwas too slight to raise a problem.

[0269] For sample #54a and comparative sample #501a, a voltage of about1 V was applied to measure the transmittance in the direction normal tothe surface of the liquid crystal cell 16 during white display. As aresult, the transmittance decreased to a level intolerable for use incomparative sample #501a. On the contrary, in sample #54a of thisexample, although a slight reduction in transmittance was observed, itwas slight enough to be tolerable for use.

[0270] (Embodiment 2)

[0271] The LCD device of Embodiment 2 has substantially the sameconfiguration as that of Embodiment 1. In Embodiment 1, the rates ofvariation of the ordinary light refractive index no and theextraordinary light refractive index ne of the liquid crystal materialwith respect to the wavelength are set to in the range in which viewingangle dependent coloring does not occur on the display screen. Instead,in Embodiment 2, in order to obtain optimal characteristics incombination with the optical phase difference compensating function ofthe optical phase plates 2 and 3, the conditions of the combination ofthe length of an alkyl chain of the liquid crystal material for theliquid crystal layer 8, the rate of variation of the ordinary lightrefractive index no of the liquid crystal material with respect to thewavelength, and rate of variation of the extraordinary light refractiveindex no of the liquid crystal material with respect to the wavelengthare set so that viewing angle dependent coloring does not occur on thedisplay screen.

[0272] More specifically, the conditions of the combination of thelength of a mean alkyl chain of the liquid crystal material, the rate ofvariation of the ordinary light refractive index no of the liquidcrystal material with respect to the wavelength, and the rate ofvariation of the extraordinary light refractive index ne of the liquidcrystal material with respect to the wavelength are set so as to satisfyat least any one of settings (1) to (3) below.

[0273] (1) In the case where the length m of a mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is m <3.40, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range:1.00 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ −0.422  m + 2.55.

[0274] More preferably, the rates of variation are set in the followingrange:1 ≤ (no(450) − no(550))/(no(550) − no(650))/(ne(450) − ne(550))/(ne(550) − ne(650)) ≤ −0.343  m + 2.26.

[0275] (2) In the case where the length m of the mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is 3.40≦m≦3.90, the rateof variation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range:0.80 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.20.

[0276] More preferably, the rates of variation are set in the followingrange:0.85 < (no(450) − no(550))/(no(550) − no(650))/(ne(450) − ne(550))/(ne(550) − ne(650)) < 1.15.

[0277] (3) In the case where the length m of a mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is m>3.90, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range:−0.422  m + 2.55 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0278] More preferably, the rates of variation are set in the followingrange:−0.343  m + 2.26 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0279] By utilizing the above ranges, in the LCD device of thisembodiment, a change in the optical phase difference between theordinary light and the extraordinary light which occurs in the LCDelement 1 depending on the viewing angle can be compensated by theoptical phase plates 2 and 3. Moreover, viewing angle dependent coloringoccurring on the liquid crystal display screen can be especiallyeffectively compensated by the liquid crystal material in the liquidcrystal layer 8. As a result, since viewing angle dependent coloring onthe display screen is effectively reduced and, at the same time, thecontrast change and the inversion phenomenon are reduced, high-qualityimages can be obtained.

[0280] Hereinbelow, the LCD device of this embodiment will be describedby way of specific examples.

EXAMPLE 6

[0281] In Example 6, in the LCD device shown in FIG. 1, a liquid crystalmaterial for the liquid crystal layer 8 was obtained by blendingmaterials represented by structural formula (2) below

[0282] so that the length m of a mean alkyl chain (C_(m)H_(2m+1)—) permole is m<3.40, and that the rate of variation among the extraordinarylight refractive indices ne(450), ne(550), and ne(650) of the liquidcrystal material for light with wavelengths of 450 nm, 550 nm, and 650nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in therange of:1.00 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ −0.422  m + 2.55.

[0283] The cell thickness of the liquid crystal cell 16 (the thicknessof the liquid crystal layer 8) was set at 5 μm. Five samples of such LCDdevices as shown in Table 6 below (samples #11b to #15b) were produced.

[0284] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle Θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis direction in the xyz coordinatesystem and the direction of the principal refractive index no is tiltedby about 20° in the direction of the arrow B from the x-axis.

[0285] For comparison, two comparative samples of LCD devices as shownin Table 6 below (comparative samples #100b and #101b) were produced inthe same manner as that used in the above samples of this example exceptthat liquid crystal materials having the setting in the range of:

1>((no(450)−no(550))/(no(550)−no(650)))/((ne(450)−ne(550))/(ne(550)−ne(650))),

[0286] or((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) > −0.422m + 2.55.

[0287] were used for the liquid crystal layer 8 of the LCD device shownin FIG. 1.

[0288] Table 6 shows the results of visual inspections performed underwhite light for samples #11b to #15b and comparative samples #100b and#101b. In Table 6, as well as Tables 7 and 8 for Examples 7 and 8, to bedescribed later,F(no(λ), ne(λ) = (((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650)))), and

[0289] the mark ◯ represents “no coloring”, Δ represents “tolerablecoloring”, and X represents 'intolerable coloring”. TABLE 6 Sample #100b#11b #12b #13b #14b #15b #101b Mean alkyl chain 3.38 3.30 3.25 3.30 3.383.35 3.30 length (m) F(no(λ), ne(λ)) 1.25 1.14 1.16 1.05 1.05 1.00 0.90Viewing angle (θ) 50° x ∘ ∘ ∘ ∘ ∘ x 60° x Δ Δ ∘ ∘ ∘ x 70° x x x ∘ ∘ ∘ x

[0290] It is found from Table 6 that in samples #13b to #15b no coloringwas observed in any direction at a viewing angle of 70°, providing goodimage quality. This indicates that especially excellent characteristicsare provided when the setting is in the range of:1 ≤ ((no(450) − no(550))/(no(550) − no(650))/(ne(450) − ne(550))/(ne(550) − ne(65))) ≤ −0.343m + 2.26.

[0291] It is also found from Table 6 that in samples #11b and #12b nocoloring was observed in any direction at a viewing angle of 50°,providing good image quality. At a viewing angle of 60°, although slightcoloring was observed when viewed from the right and left sides, it wasin such a level that was tolerable for use.

[0292] As for comparative samples #100b and #101b, yellow to orangecoloring intolerable for use was observed even at a viewing angle of 50°when viewed from the right and left sides.

[0293] Substantially the same results were obtained for samples of LCDdevices produced in the same manner as that used in samples #11b to #15band comparative samples #100b and #101b, except that the optical phaseplates 2 and 3 were made of a discotic liquid crystal material appliedto a transparent support and crosslinked in a hybrid orientation.

EXAMPLE 7

[0294] In Example 7, in the LCD device shown in FIG. 1, a liquid crystalmaterial for the liquid crystal layer 8 was set so that: the length m ofa mean alkyl chain (C_(m)H_(2m+1)—) per mole is in the range of3.40≦m≦3.90: and the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) of the liquid crystalmaterial for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are in therange of:0.08 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.20.

[0295] Such a liquid crystal material was prepared by blending thematerials shown in Example 6.

[0296] The cell thickness of the liquid crystal cell 16 was set at 5 μm.Five samples of such LCD devices as shown in Table 7 below (samples #21bto #25b) were produced.

[0297] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis direction in the xyz coordinatesystem and the direction of the principal refractive index no is tiltedby about 20° in the direction of the arrow B from the x-axis.

[0298] For comparison, two comparative samples of LCD devices as shownin Table 7 below (comparative samples #200b and #201b) were produced inthe same manner as that used in the above samples of this example exceptthat liquid crystal materials having the setting in the range of:0.80 > ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))), ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) > 1.20.

[0299] or

[0300] were used for the liquid crystal layer 8 of the LCD device shownin FIG. 1.

[0301] Table 7 below shows the results of visual inspections performedunder white light for samples #21b to #25b and comparative samples #200band #201b. TABLE 7 Sample #200b #21b #22b #23b #24b #25b #201b Meanalkyl chain 3.90 3.55 3.80 3.68 3.60 3.45 3.40 length (m) F(no(λ),ne(λ)) 0.75 0.85 0.90 1.00 1.15 1.15 1.25 Viewing angle (θ) 50° x ∘ ∘ ∘∘ ∘ x 60° x Δ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0302] It is found from Table 7 that in samples #22b to #24b no coloringwas observed in any direction at a viewing angle of 70°, providing goodimage quality. This indicates that especially excellent characteristicsare provided when the setting is in the range of:0.85 < (no(450) − no(550))/(no(550) − no(650))/(ne(450) − ne(550))/(ne(550) − ne(650)) < 1.15.

[0303] It is also found from Table 7that in samples #21b and #25b nocoloring was observed in any direction at a viewing angle of 50°,providing good image quality. At a viewing angle of 60°, although slightcoloring was observed when viewed from the right and left sides, it wasin such a level that was tolerable for use.

[0304] As for comparative samples #200b and #201b, yellow to orangecoloring intolerable for use was observed even at a viewing angle of 50°when viewed from the right and left sides.

[0305] Substantially the same results were obtained for samples of LCDdevices produced in the same manner as that used in samples #21b to #25band comparative samples #200b and #201b, except that the optical phaseplates 2 and 3 were made of a discotic liquid crystal material appliedto a transparent support and crosslinked in a hybrid orientation.

EXAMPLE 8

[0306] In Example 8, in the LCD device shown in FIG. 1, a liquid crystalmaterial for the liquid crystal layer 8 was set so that: the length m ofa mean alkyl chain (C_(m)H_(2m+1)—) per mole is in the range of m>3.90:and the rate of variation among the extraordinary light refractiveindices ne(450), ne(550), and ne(650) of the liquid crystal material forlight with wavelengths of 450 nm, 550 nm, and 650 nm, respectively, andthe rate of variation among the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, are in the range of:−0.422m + 2.55 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0307] Such a liquid crystal material was prepared by blending thematerials shown in Example 6.

[0308] The cell thickness of the liquid crystal cell 16 was set at 5 μm.Five samples of such LCD devices as shown in Table 8 below (samples #31bto #35b) were produced.

[0309] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis direction in the xyz coordinatesystem and the direction of the principal refractive index no is tiltedby about 20° in the direction of the arrow B from the x-axis.

[0310] For comparison, two comparative samples of LCD devices as shownin Table 8 below (comparative samples #300b and #301b) were produced inthe same manner as that used in the above samples of this example exceptthat liquid crystal materials having the setting in the range of:−0.422m + 2.55 > ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))), or((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) > 1.

[0311] were used for the liquid crystal layer 8 of the LCD device shownin FIG. 1.

[0312] Table 8 shows the results of visual inspections performed underwhite light for samples #31b to #35b and comparative samples #300b and#301b. TABLE 8 Sample #300b #31b #32b #33b #34b #35b #301b Mean alkylchain 4.60 5.00 4.20 4.60 4.50 5.00 4.75 F(no(λ), ne(λ)) 0.50 0.44 0.800.70 0.89 1.00 1.10 Viewing angle (θ) 50° x ∘ ∘ ∘ ∘ ∘ x 60° x x Δ ∘ ∘ ∘x 70° x x x ∘ ∘ ∘ x

[0313] It is found from Table 8 that in samples #33b to #35b no coloringwas observed in any direction at a viewing angle of 70°, providing goodimage quality. This indicates that especially excellent characteristicsare provided when the setting is in the range of:−0.343m + 2.26 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.

[0314] In sample #31b, no coloring was observed in any direction at aviewing angle of 50° or less, providing good image quality. At a viewingangle of 60°, a level of coloring intolerable for use was observed whenviewed from the right and left sides.

[0315] In sample #32b, no coloring was observed in any direction at aviewing angle of 50° or less, providing good image quality. At a viewingangle of 60°, although slight coloring was observed when viewed from theright and left sides, it was in such a level that was tolerable for use.

[0316] As for comparative samples #300b and #301b, yellow to orangecoloring intolerable for use was observed even at a viewing angle of 50°when viewed from the right and left sides.

[0317] Substantially the same results were obtained for samples of LCDdevices produced in the same manner as that used in samples #31b to #35band comparative samples #300b and #301b, except that the optical phaseplates 2 and 3 were made of a discotic liquid crystal material appliedto a transparent support and crosslinked in a hybrid orientation.

EXAMPLE 9

[0318] In Example 9, three samples (samples #41b to #43b) of the LCDdevice shown in FIG. 1 were produced using liquid crystal materials ofwhich the values of the refractive index anisotropy Δn(550) for lightwith a wavelength of 550 nm were set at 0.070, 0.080, and 0.095,respectively. The cell thickness of the liquid crystal cell 16 of thesesamples was 5 μm. The mean alkyl chain length m; and the rates ofvariation of the ordinary light refractive index no and theextraordinary light refractive index ne (represented by F(no(λ), ne(λ)))of each sample are shown in Table 9 below. TABLE 9 Sample #41b #42b #43b#401b #402b Mean alkyl chain 3.38 3.68 4.60 4.50 4.60 length (m)F(no(λ), ne(λ)) 1.05 1.00 0.70 0.89 0.70

[0319] Such a liquid crystal material was prepared by blending thematerials shown in Example 6.

[0320] As the optical phase plates 2 and 3, those including a discoticliquid crystal material in a tilted orientation as in Example 6 wereused.

[0321] For comparison, two comparative samples of LCD devices as shownin Table 9 above (comparative samples #401b and #402b) were produced inthe same manner as that used in the above samples of this example,except that liquid crystal materials of which the values of therefractive index anisotropy Δn for light with a wavelength of 550 nmwere set at 0.060 and 0.120, respectively.

[0322] The LCD devices of samples #41b to #43b and comparative samples#401b and #402b were measured for the viewing angle dependence using themeasurement system as shown in FIG. 5 including the light-receivingelement 18, the amplifier 19, and the recording device 20.

[0323] The LCD devices of samples #41b to #43b and comparative samples#401b and #402b were placed in the above measurement system, to measurethe relationship between the voltage applied to the LCD devices and theoutput level of the light-receiving element 18 when the light-receivingelement 18 was fixed at a constant angle φ.

[0324] It was assumed that the x-axis direction is toward the lower sideof the screen and the y-axis direction is toward the left side thereof.The measurement was performed by changing the position of thelight-receiving element 18 among positions at an angle φ of 50° in theupward direction (negative viewing direction), the right direction, andthe left direction.

[0325] The measurement results of samples #41b to #43b are shown inFIGS. 8A to 8C, while those of comparative samples #401b and #402b areshown in FIGS. 9A to 9C. FIGS. 8A to 8C and 9A to 9C are graphs of thelight transmittance of the LCD devices with respect to the voltageapplied thereto (transmittance vs. applied voltage characteristics):FIGS. 8A and 9A show the results obtained when measured from the upperside as is viewed from FIG. 5; FIGS. 8B and 9B show the results obtainedwhen measured from the right side as is viewed from FIG. 5: and FIGS. 8Cand 9C show the results obtained when measured from the left side as isviewed from FIG. 5.

[0326] Referring to FIGS. 8A to 8C, curves L1 b, L4 b, and L7 b (theone-dot dash lines) represent sample #41b which uses a liquid crystalmaterial with Δn(550) of 0.070 for the liquid crystal layer 8, curves L2b, L5 b, and L8 b (the solid lines) represent sample #42b which uses aliquid crystal material with Δn(550) of 0.080 for the liquid crystallayer 8, and curves L3 b, L6 b, and L9 b (the dashed lines) representsample #43b which uses a liquid crystal material with Δn(550) of 0.095for the liquid crystal layer 8. Referring to FIGS. 9A to 9C, curves L10b, L12 b, and L14 b (the solid lines) represent comparative sample #401bwhich uses a liquid crystal material with Δn(550) of 0.060 for theliquid crystal layer 8, and curves L11 b, L13 b, and L15 b (the dashedlines) represent sample #402b which uses a liquid crystal material withΔn(550) of 0.120 for the liquid crystal layer 8.

[0327] As for the transmittance vs. applied voltage characteristicsmeasured from the upper side, as shown by curves L1 b to L3 b in FIG.8A, it was confirmed that in samples #41b to #43b as the voltageincreased the transmittance sufficiently decreased. On the contrary, incomparative sample #402b, as shown by curve L11 b in FIG. 9A, as thevoltage increased the transmittance did not sufficiently decrease. Incomparative sample #401b, as shown by curve L10 b in FIG. 9A, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0328] Likewise, as for the transmittance vs. applied voltagecharacteristics measured from the right side, as shown by curves L4 b toL6 b in FIG. 8B, it was confirmed that in samples #41b to #43b as thevoltage increased the transmittance decreased to nearly zero. Incomparative sample #401b, as shown by curve L12 b in FIG. 9B, as thevoltage increased the transmittance decreased to nearly zero. However,in comparative sample #402b, as shown by curve L13 b in FIG. 9B, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0329] Likewise, as for the transmittance vs. applied voltagecharacteristics measured from the left side, as shown by curves L7 b toL9 b in FIG. 8C, it was confirmed that in samples #41b to #43b as thevoltage increased the transmittance decreased to nearly zero. Incomparative sample #401b, as shown by curve L14 b in FIG. 9C, as thevoltage increased the transmittance decreased to nearly zero. However,in comparative sample #402b, as shown by curve L15 b in FIG. 9C, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0330] Visual inspection was performed for samples #41b to #43b andcomparative samples #401b and #402b under white light. As a result, forsamples #41b to #43b of this example and comparative sample #401b, nocoloring was observed in any direction at a viewing angle of 50° orless, providing good image quality.

[0331] For comparative sample #402b, however, yellow to orange coloringwas observed when viewed from the right and left sides at a viewingangle of 50°.

[0332] From the above results, the following are recognized: As shown inFIGS. 8A to 8C, for the samples of the LCD device of this example(samples #41b to #43b) using, for the liquid crystal layer 8, a liquidcrystal material of which the values of the refractive index anisotropyΔn(550) for light with a wavelength of 550 nm were set at 0.070, 0.080,and0.095, as the applied voltage was increased, the transmittancesufficiently decreased, preventing an inversion phenomenon fromoccurring and thus widening the angle of field. Moreover, since nocoloring was observed, the display quality of the LCD devicessignificantly improved.

[0333] On the contrary, as shown in FIGS. 9A to 9C, as for thecomparative samples of the LCD devices (comparative samples #401b and#402b) using liquid crystal materials of which the values of therefractive index anisotropy Δn(550) for 550 nm light were set at 0.060and 0.120, the viewing angle dependence was not sufficiently improved.

[0334] The same results as those described above were also obtained forsamples of LCD devices produced in the same, manner as that used insamples #41b to #43b and comparative samples #401b and #402b, exceptthat the optical phase plates 2 and 3 were made of a discotic liquidcrystal material applied to a transparent support and crosslinked in ahybrid orientation.

[0335] The dependence of the transmittance vs. applied voltagecharacteristics on the tilt angle θ was examined by changing the tiltangle θ of the index ellipsoid of the optical phase plate 2 or 3. As aresult, essentially the same results as those described above wereobtained, irrespective of the orientation state of the discotic liquidcrystal material used for the optical phase plate 2 or 3, if the angle θis in the range of 15°≦θ≦75°. If the angle θ is less than 15° or exceeds75°, it was confirmed that the angle of field in the negative viewingdirection is not widened.

[0336] The dependence of the transmittance vs. applied voltagecharacteristics on the second retardation value (na−nb)×d was examinedby changing the second retardation value. As a result, essentially thesame results as those described above were obtained, irrespective of theorientation state of the discotic liquid crystal material used for theoptical phase plates 2 and 3, if the second retardation value is in therange between 80 nm and 250 nm inclusive. If the second retardationvalue is less than 80 nm or exceeds 250 nm, it was confirmed that theangle of field in the lateral (right and left) directions is notwidened.

[0337] Additional three samples of the LCD device shown in FIG. 1(samples #44b to #46b) were produced based on the results of the visualinspection of comparative samples #401b and #402b in the same manner asthat used for samples #41b to #43b except that liquid crystal materialsof which the values of the refractive index anisotropy for 550 nm lightwere set at 0.065, 0.100, and 0.115 were used for the liquid crystallayer 8.

[0338] Samples #44b to #46b of the LCD devices were placed in themeasurement system shown in FIG. 5. The relationship between the voltageapplied to the respective LCD devices and the output level of thelight-receiving element 18 obtained when the light-receiving element 18was fixed at a constant angle φ was measured, and the visual inspectionunder white light was performed.

[0339] The results of the above measurement and inspection are asfollows. In samples #45b and #46b of this example in which the values ofthe refractive index anisotropy Δn(550) were set at 0.100 and 0.115, aslight increase in transmittance was observed as the voltage wasincreased when measured from the right and left sides at an angle φ of50°. However, with no inversion phenomenon observed in the visualinspection, such a level of increase in the transmittance was tolerablefor use. When measured from the upper side, samples #45b and #46b had noproblem.

[0340] In sample #44b in which the value of the refractive indexanisotropy Δn(550) was set at 0.065 for light with a wavelength of 550nm, as the voltage increased, the transmittance initially decreased andthen increased again, causing an inversion phenomenon, when measuredfrom the upper side, as in comparative sample #401b described above.However, the degree of the increase in transmittance was small enough tobe tolerable for use, compared with the case of comparative sample #401b(L10 b) shown in FIG. 9A. When measured from the right and left sides,the results had no problem.

[0341] In the visual inspection, slight yellow to orange coloring wasobserved in samples #45b and #46b, although it was too slight to raise aproblem. For sample #44b, slight blue coloring was observed, although itwas too slight to raise a problem.

[0342] For sample #44b and comparative sample #401b, a voltage of about1 V was applied to measure the transmittance in the direction normal tothe surface of the liquid crystal cell 16 during white display. As aresult, the transmittance decreased to a level intolerable for use incomparative sample #401b. On the contrary, in sample #44b of thisexample, although a slight reduction in the transmittance was observed,it was slight enough to be tolerable for use.

[0343] (Embodiment 3)

[0344]FIG. 10 is a sectional view of an LCD device of an embodimentaccording to the present invention. The LCD device of this embodimentincludes a liquid crystal cell 16 including an LCD element 1, a pair ofoptical phase plates 2 and 3, and a pair of, polarizing plates(polarizers) 4 and 5 and a driving circuit 17.

[0345] The LCD element 1 includes a pair of electrode substrates 6 and 7and a liquid crystal layer 8 interposed therebetween. The electrodesubstrate 6 includes a base glass substrate (transparent substrate) 9,transparent electrodes 10 made of ITO (indium tin oxide) formed on thesurface of the glass substrate 9 facing the liquid crystal layer 8, andan alignment film 11 formed on the transparent electrodes 10. Theelectrode substrate 7 includes a base glass substrate (transparentsubstrate) 12, transparent electrodes 13 made of ITO (indium tin oxide)formed on the surface of the glass substrate 12 facing the liquidcrystal layer 8, and an alignment film 14 formed on the transparentelectrodes 13. The transparent electrodes 10 and 13 are connected to thedriving circuit 17.

[0346] Although only one pixel region is shown in FIG. 10 forsimplification, it should be understood that stripe-shaped transparentelectrodes 10 and 13, having a predetermined width, are formed oversubstantially the entire surface of a display portion of the LCD device1 so that the transparent electrodes 10 on the glass substrate 9 and thetransparent electrodes 13 on the glass substrate 12 cross each other(perpendicular to each other in this example) as is viewed at a positionnormal to the substrate surface.

[0347] The intersections of the transparent electrodes 10 and 13correspond respective pixel regions, which are arranged in a matrix overthe entire LCD device.

[0348] The electrode substrates 6 and 7 are bonded together with a sealresin 15, and a liquid crystal material is sealed in a space enclosed bythe electrode substrates 6 and 7 and the seal resin 15 to form theliquid crystal layer 8. A voltage based on display data is applied tothe liquid crystal layer 8 from the driving circuit 17 via thetransparent electrodes 10 and 13.

[0349] Each of the alignment films 11 and 14 formed on the sides of theelectrode substrates 6 and 7 facing the liquid crystal layer 8,respectively, has two portions having different alignment features foreach pixel region, so that these portions have different pretilt anglesfor liquid crystal molecules or the pretilt directions of liquid crystalmolecules in these portions are opposite to each other with respect tothe direction normal to the substrate surface. This enables a portion ofthe liquid crystal layer 8 corresponding to one pixel region to bedivided into a first liquid crystal molecule orientation domain 8 a anda second liquid crystal molecule orientation domain 8 b having differentorientation states of liquid crystal molecules.

[0350] Furthermore, in this embodiment, in order to improve the viewingangle characteristic obtained when the viewing angle is tilted in theupward and downward directions and right and left directions, in onepixel region, the first liquid crystal molecule orientation domain 8 ais made larger than the second liquid crystal region 8 b as shown inFIGS. 10 and 11.

[0351]FIG. 11 is a schematic view of a liquid crystal panel as is viewedfrom a position normal to the panel. An arrow P₁ represents a rubbingdirection in the portion of the alignment film 11 corresponding to thefirst liquid crystal molecule orientation domain 8 a, an arrow P₂represents a rubbing direction in the portion of the alignment film 11corresponding to the second liquid crystal molecule orientation domain 8b, an arrow P₃ represents a rubbing direction in the portion of thealignment film 14 corresponding to the first liquid crystal moleculeorientation domain 8 a, and an arrow P₄ represents a rubbing directionin the portion of the alignment film 14 corresponding to the secondliquid crystal molecule orientation domain 8 b. As shown in FIG. 11, byrubbing each of the alignment films 11 and 14 so that the rubbingdirections are different between the portions of the alignment filmcorresponding to the liquid crystal molecule orientation domains 8 a and8 b having different areas, the portion of the liquid crystal layercorresponding to one pixel region can be divided into the liquid crystalmolecule orientation domains 8 a and 8 b having different orientationstates at an unequal division ratio. One alignment film alone may beprovided for the LCD device.

[0352] The optical phase plates 2 and 3 are disposed between the LCDelement 1 and the polarizing plates 4 and 5, respectively, located onboth surfaces of the LCD element 1. Each of the optical phase plates 2and 3 includes a support made of a transparent organic polymer and adiscotic liquid crystal material crosslinked to the support in a tiltedor hybrid orientation, so that an index ellipsoid thereof is tilted aswill be described later.

[0353] The support of the optical phase plates 2 and 3 is preferablymade of triacetyl cellulose (TAC) which is generally used for apolarizing plate. Using this material, a reliable optical phase plate isobtained. Other materials suitable for the support include transparentand colorless organic polymer films with excellent environmentresistance and chemical resistance, such as polycarbonate (PC) andpolyethylene terephthalate (PET) films.

[0354] As shown in FIG. 3, in relation with Embodiment 1, each of theoptical phase plates 2 and 3 has the principal refractive indices na,nb, and nc representing three different directions.

[0355] The direction of the principal refractive index na is identicalto the y-axis in the rectangular coordinate system xyz, which isparallel to the surface of the optical phase plates 2 and 3 (parallel tothe screen). The direction of the principal refractive index nb istilted by an angle of θ in the direction of an arrow A from the z-axiswhich is normal to the surface of the optical phase plates 2 and 3(perpendicular to the screen) with respect to the direction of theprincipal refractive index na as an axis. The direction of the principalrefractive index no is tilted by the angle θ in the direction of anarrow B from the x-axis which is parallel to the surface of the opticalphase plates 2 and 3 (parallel to the screen) with respect to thedirection of the principal refractive index na as an axis.

[0356] The three principal refractive indices na, nb, and nc have therelationship of na=nc>nb. In this case, since the optical phase plate 2,3 is uniaxial, having a single optical axis, the refractive indexanisotropy is negative.

[0357] A first retardation value of the optical phase plates 2 and 3 areexpressed by the product of the difference (refractive index anisotropyΔn) between the principal refractive indices na and nc and the thicknessd of the optical phase plate ((nc−na)×d). Since na=nc, the firstretardation value is substantially 0 nm. A second retardation value ofthe optical phase plates 2 and 3 are expressed by the product of thedifference (refractive index anisotropy Δn) between the principalrefractive indices na and nb and the thickness d of the optical phaseplate ((na−nb)×d). The second retardation value is preferably set in therange between 80 nm and 250 nm inclusive. Setting the value in thisrange ensures that the optical phase plates 2 are 3 provide the opticalphase plate compensating function.

[0358] In the LCD device of this embodiment, the LCD element 1, theoptical phase plates 2 and 3, and the polarizing plates 4 and 5 arearranged as shown in FIG. 12. In FIG. 12, the liquid crystal moleculeorientation domain 8 b is omitted for simplification.

[0359] The polarizing plate 4 is arranged so that an absorption axis AX₁thereof is parallel to the rubbing direction P₁ of the portion of thealignment film 11 corresponding to the liquid crystal moleculeorientation domain 8 a described above, while the polarizing plate 5 isarranged so that an absorption axis AX₂ thereof is parallel to therubbing direction P₃ of the portion of the alignment film 14corresponding to the liquid crystal molecule orientation domain 8 a.

[0360] The optical phase plate 2 is arranged so that a direction D₁(corresponding to the direction D described with reference to FIG. 3) isparallel to the rubbing direction P₁ of the portion of the alignmentfilm 11 corresponding to the liquid crystal molecule orientation domain8 a, while the optical phase plate 3 is arranged so that a direction D₂(corresponding to the direction D described with reference to FIG. 3) isparallel to the rubbing direction P₂ of the portion of the alignmentfilm 14 corresponding to the liquid crystal molecule orientation domain8 a.

[0361] As for the liquid crystal layer 8, the rates of variation of theordinary light refractive index no and the extraordinary lightrefractive index ne of the liquid crystal material with respect to thewavelength are preset to be in a predetermined range in which viewingangle dependent coloring does not occur on the display screen, inconsideration of the matching with the wavelength dependence of therefractive index of the optical phase plates 2 and 3.

[0362] More specifically, the rates of variation of the ordinary lightrefractive-index no and the extraordinary light refractive index ne ofthe liquid crystal material with respect to the wavelength are set so asto satisfy at least one of setting ranges (a) and (b) in each of thefollowing conditions (1) and (2).

[0363] (1) When the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00,

[0364] (a) the rate of variation among the ordinary light refractiveindices no(450), no(550), and no(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, is set in the range of:

1.65≦(no(450)−no(550))/(no(550)−no(650))≦2.40.

[0365] More preferably, the rate of variation is set in the followingrange:

1.85≦(no(450)−no(550))/(no(550)−no(650))≦2.20.

[0366] (b) The rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, is set in therange of

1.70≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.30.

[0367] More preferably, the rate of variation is set in the followingrange:

1.85≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.10.

[0368] (2) When the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00,

[0369] (a) The rate of variation among the ordinary light refractiveindices no(450), no(550), and no(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, is set in the range of:

1.00≦(no(450)−no(550))/(no(550)−no(650))≦1.65.

[0370] More preferably, the rate of variation is set in the followingrange:

1.15≦(no(450)−no(550))/(no(550)−no(650))≦1.45.

[0371] (b) The rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, is set in therange of:

1.20≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.70.

[0372] More preferably, the rate of variation is set in the followingrange:

1.35≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.60.

[0373] By utilizing the above ranges, in the LCD device of thisembodiment, high-quality display images with a wide angle of fieldwithout coloring when the viewing angle is dropped or during gray scaledisplay are obtained.

[0374] Hereinbelow, the LCD device of this embodiment will be describedby way of specific examples.

EXAMPLE 10

[0375] In Example 10, in the LCD device shown in FIG. 10, a liquidcrystal material for the liquid crystal layer 8 was set so that: theextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, are in the range of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00; and

[0376] the rate of variation among the extraordinary light refractiveindices ne(450), ne(550), and ne(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, is in the range of:

1.70≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.30.   (A)

[0377] Such a liquid crystal material was prepared by blending thematerials represented by structural formula (3) below:

[0378] For the alignment films 11 and 14, Optomer AL, manufactured byJapan Synthetic Rubber Co., Ltd., was used. The division ratio of thefirst liquid crystal molecule orientation domain 8 a to the secondliquid crystal molecule orientation domain 8 b of the portion of theliquid crystal layer 8 corresponding to one pixel region was set at17:3. The cell thickness of the liquid crystal cell 16 (the thickness ofthe liquid crystal layer 8) was set at 5 μm. Five samples of such LCDdevices as shown in Table 10 below (samples #11c to #15c) were produced.

[0379] In these samples, the optical phase plates 2 and 3 were formed inthe following manner. A discotic liquid crystal material was applied toa transparent support (made of triacetyl cellulose (TAC), for example).The discotic liquid crystal material was crosslinked in a tiltedorientation so that the first retardation value (nc−na)×d is 0 nm whilethe second retardation value (na−nb)×d is 100 nm, and that the tiltangle θ of a tilted index ellipsoid is 20° where the direction of theprincipal refractive index nb shown in FIG. 3 is tilted by about 20° inthe direction of the arrow A from the z-axis in the xyz coordinatesystem and the direction of the principal refractive index no is tiltedby about 20° in the direction of the arrow B from the x-axis.

[0380] For comparison, two comparative samples of LCD devices as shownin Table 10 below (comparative samples #201c and #202c) were produced inthe same manner as that in the above samples of this example except thatliquid crystal materials having a rate of variation((ne(450)−ne(550)/(ne(550)−ne(650)) of 1.60 and 2.40, which are outsidethe above range (A), were used for the liquid crystal layer 8 of the LCDdevice shown in FIG. 10.

[0381] Table 10 shows the results of visual inspections of color hue atviewing angles of 50°, 60°, and 70° performed for samples #11c to #15cand comparative samples #201c and #202c. In Table 10, as well as Tables11 to 13 for Examples 11 to 13, to be described later, the mark ◯represents “no coloring”, A represents “tolerable coloring”, and Xrepresents “intolerable coloring”. TABLE 10 Sample #201c #11c #12c #13c#14c #15c #202c Viewing angle (ne(450) − ne(550))/(ne(550) − ne(650))(θ) 1.60 1.70 1.85 1.90 2.10 2.30 2.40 50° x ∘ ∘ ∘ ∘ ∘ x 60° x Δ ∘ ∘ ∘ Δx 70° x x ∘ ∘ ∘ x x

[0382] It is found from Table 10 that in samples #12c to #14c nocoloring was observed even when the viewing angle was dropped to 70°,providing good image quality. This indicates that coloring is furtherreduced and especially excellent characteristics are provided in therange of the rate of variation of:

1.85≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.10.

[0383] As for samples #11c and #15c, although coloring was observed atviewing angles of 60° and 70°, no coloring was observed at a viewingangle of 50° or less, providing good display characteristics of a leveltolerable for use.

[0384] As for comparative samples #201c and #202c, however, coloring waseminently observed when the viewing angle is dropped to 50°, providingdisplay characteristics of a level intolerable for use.

EXAMPLE 11

[0385] In Example 11, in the LCD device shown in FIG. 10, a liquidcrystal material for the liquid crystal layer 8 was set so that: theextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, are in the range of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00; and

[0386] the rate of variation among the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, is in the range of:

1.65≦(no(450)−no(550))/(no(550)−no(650))≦2.40.   (B)

[0387] Such a liquid crystal material was prepared by blending thematerials shown in Example 10.

[0388] For the alignment films 11 and 14, Optomer AL, manufactured byJapan Synthetic Rubber Co., Ltd., was used. The division ratio of thefirst liquid crystal molecule orientation domain 8 a to the secondliquid crystal molecule orientation domain 8 b of the portion of theliquid crystal layer 8 corresponding to one pixel region was set at17:3. The cell thickness of the liquid crystal cell 16 (the thickness ofthe liquid crystal layer 8) was set at 5 μm. Five samples of such LCDdevices as shown in Table 11 below (samples #21c to #25c) were produced.

[0389] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis in the xyz coordinate systemand the direction of the principal refractive index no is tilted byabout 20° in the direction of the arrow B from the x-axis.

[0390] For comparison, two comparative samples of LCD devices as shownin Table 11 below (comparative samples #301c and #302c) were produced inthe same manner as that in the above samples of this example except thatliquid crystal materials having a rate of variation((no(450)−no(550)/(no(550)−no(650)) of 1.55 and 2.50, which are outsidethe above range (B), were used for the liquid crystal layer 8 of the LCDdevice shown in FIG. 10.

[0391] Table 11 shows the results of visual inspections of color hue atviewing angles of 50°, 60°, and 70° performed for samples #21c to #25cand comparative samples #301c and #302c. TABLE 11 Sample #301c #21c #22c#23c #24c #25c #302c Viewing angle (no(450) − no(550))/(no(550) −no(650)) (θ) 1.55 1.65 1.85 2.05 2.20 2.40 2.50 50° x ∘ ∘ ∘ ∘ ∘ x 60° xΔ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0392] It is found from Table 11 that in samples #22c to #24c nocoloring was observed even when the viewing angle was dropped to 70°,providing good image quality. This indicates that coloring is furtherreduced and especially excellent characteristics are provided in therange of the rate of variation of:

1.85≦(no(450)−no(550))/(no(550)−no(650))≦2.20.

[0393] As for samples #21c and #25c, although coloring was observed atviewing angles of 60° and 70°, no coloring was observed at a viewingangle of 50° or less, providing good display characteristics of a leveltolerable for use.

[0394] As for comparative samples #301c and #302c, however, coloring waseminently observed when the viewing angle is dropped to 50°, providingdisplay characteristics of a level intolerable for use.

EXAMPLE 12

[0395] In Example 12, in the LCD device shown in FIG. 10, a liquidcrystal material for the liquid crystal layer 8 was set so that: theextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, are in the range of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00; and

[0396] the rate of variation among the extraordinary light refractiveindices ne(450), ne(550), and ne(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, is in the range of:

1.20≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.70.   (C)

[0397] Such a liquid crystal material was prepared by blending thematerials shown in Example 10.

[0398] For the alignment films 11 and 14, Optomer AL, manufactured byJapan Synthetic Rubber Co. Ltd., was used. The division ratio of thefirst liquid crystal molecule orientation domain 8 a to the secondliquid crystal molecule orientation domain 8 b of the portion of theliquid crystal layer 8 corresponding to one pixel region was set at17:3. The cell thickness of the liquid crystal cell 16 (the thickness ofthe liquid crystal layer 8) was set at 5 μm. Five samples of such LCDdevices as shown in Table 12 below (samples #31c to #35c) were produced.

[0399] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis in the xyz coordinate systemand the direction of the principal refractive index no is tilted byabout 20° in the direction of the arrow B from the x-axis.

[0400] For comparison, two comparative samples of LCD devices as shownin Table 12 below (comparative samples #401c and #402c) were produced inthe same manner as that in the above samples of this example, exceptthat liquid crystal materials having a rate of variation((ne(450)−ne(550)/(ne(550)−ne(650)) of 1.10 and 1.80, which are outsidethe above range (C), were used for the liquid crystal layer 8 of the LCDdevice shown in FIG. 10.

[0401] Table 12 shows the results of visual inspections of color hue atviewing angles of 50°, 60°, and 70° performed for samples #31c to #35cand comparative samples #401c and #402c. TABLE 12 Sample #401c #31c #32c#33c #34c #35c #402c Viewing angle (ne(450) − ne(550))/(ne(550) −ne(650)) (θ) 1.10 1.20 1.35 1.50 1.60 1.70 1.80 50° x ∘ ∘ ∘ ∘ ∘ x 60° xΔ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0402] It is found from Table 10 that in samples #32c to #34c nocoloring was observed even when the viewing angle was dropped to 70°,providing good image quality. This indicates that coloring is furtherreduced and especially excellent characteristics are provided in therange of the rate of variation of:

1.35≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.60.

[0403] As for samples #31c and #35c, although coloring was observed atviewing angles of 60° and 70°, no coloring was observed at a viewingangle of 50° or less, providing good display characteristics of a leveltolerable for use.

[0404] As for comparative samples #401c and #402c, however, coloring waseminently observed when the viewing angle is dropped to 50°, providingdisplay characteristics of a level intolerable for use.

EXAMPLE 13

[0405] In Example 13, in the LCD device shown in FIG. 10, a liquidcrystal material for the liquid crystal layer 8 was set so that: theextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, are in the range of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00; and

[0406] the rate of variation among the ordinary light refractive indicesno(450), no(550), and no(650) for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, is in the range of:

1.00≦(no(450)−no(550))/(no(550)−no(650))≦1.65.   (D)

[0407] Such a liquid crystal material was prepared by blending thematerials shown in Example 10.

[0408] For the alignment films 11 and 14, Optomer AL, manufactured byJapan Synthetic Rubber Co., Ltd., was used. The division ratio of thefirst liquid crystal molecule orientation domain 8 a to the secondliquid crystal molecule orientation domain 8 b of the portion of theliquid crystal layer 8 corresponding to one pixel region was set at17:3. The cell thickness of the liquid crystal cell 16 (the thickness ofthe liquid crystal layer 8) was set at 5 μm. Five samples of such LCDdevices as shown in Table 13 below (samples #41c to #45c) were produced.

[0409] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis in the xyz coordinate systemand the direction of the principal refractive index no is tilted byabout 20° in the direction of the arrow B from the x-axis.

[0410] For comparison, two comparative samples of LCD devices as shownin Table 13 below (comparative samples #501c and #502c) were produced inthe same manner as that in the above samples of this example except thatliquid crystal materials having a rate of variation((no(450)−no(550)/(no(550)−no(650)) of 0.90 and 1.75, which are outsidethe above range (D), were used for the liquid crystal layer 8 of the LCDdevice shown in FIG. 10.

[0411] Table 13 shows the results of visual inspections of color hue atviewing angles of 50°, 60°, and 70° performed for samples #41c to #45cand comparative samples #501c and #502c. TABLE 13 Sample #501c #41c #42c#43c #44c #45c #502c Viewing angle (no(450) − no(550))/(no(550) −no(650)) (θ) 0.90 1.00 1.15 1.30 1.45 1.65 1.75 50° x ∘ ∘ ∘ ∘ ∘ x 60° xΔ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0412] It is found from Table 13 that in samples #42c to #44c nocoloring was observed even when the viewing angle was dropped to 70°,providing good image quality. This indicates that coloring is furtherreduced and especially excellent characteristics are provided in therange of the rate of variation of:

1.15≦(no(450)−no(550))/(no(550)−no(650))≦1.45.

[0413] As for samples #41c and #45c, although coloring was observed atviewing angles of 60° and 70°, no coloring was observed at a viewingangle of 50° or less, providing good display characteristics of a leveltolerable for use.

[0414] As for comparative samples #501c and #502c, however, coloring waseminently observed when the viewing angle is dropped to 50°, providingdisplay characteristics of a level intolerable for use.

EXAMPLE 14

[0415] In Example 14, three samples (samples #51c to #53c) of the LCDdevice shown in FIG. 10 were produced in the following manner. OptomerAL manufactured by Japan Synthetic Rubber Co., Ltd. was used for thealignment films 11 and 14. Liquid crystal materials of which the valuesof the refractive index anisotropy Δn(550) for light with a wavelengthof 550 nm were set at 0.070, 0.080, and 0.095, respectively, were usedfor the liquid crystal layer 8. The division ratio of liquid crystalmolecule orientation domains having different orientation states of eachportion of the liquid crystal layer 8 corresponding to one pixel regionwas set at 17:3. The cell thickness of the liquid crystal cell 16 ofthese samples was 5 μm. The rates of variation of the ordinary lightrefractive index no and the extraordinary light refractive index ne ofeach sample were set as shown in Table 14 below. TABLE 14 Sample #601c#51c #52c #53c #602c (ne(450) − ne(550))/(ne(550) − ne(650)) 1.85 1.351.50 1.60 1.90 (no(450) − no(550))/(no(550) − no(650)) 1.85 1.15 1.301.45 2.05

[0416] As the optical phase plates 2 and 3, those including a discoticliquid crystal material in a tilted orientation as in Example 10 wereused.

[0417] For comparison, two comparative samples of LCD devices(comparative samples #601c and #602c) were produced in the same manneras that used in the above samples of this example, except that liquidcrystal materials of which the values of the refractive index anisotropyAn for light with a wavelength of 550 nm were set at 0.060 and 0.120,respectively.

[0418] The LCD devices of samples #51c to #53c and comparative samples#601c and #602c were measured for the viewing angle dependence using themeasurement system as shown in FIG. 5 described above including thelight-receiving element 18, the amplifier 19, and the recording device20.

[0419] The LCD devices of samples #51c to #53c and comparative samples#601c and #601c were placed in the above measurement system, to measurethe relationship between the voltage applied to the LCD devices and theoutput level of the light-receiving element 18 when the light-receivingelement 18 was fixed at a constant angle φ.

[0420] It was assumed that the x-axis direction is toward the lower sideof the screen and the y-axis direction is toward the left side thereof.The measurement was performed by changing the position of thelight-receiving element 18 among positions at an angle φ of 50° in theupward direction (negative viewing direction), the right direction, andthe left direction.

[0421] The measurement results of samples #51c to #53c are shown inFIGS. 13A to 13C, while those of comparative samples #601c and #602c areshown in FIGS. 14A to 14C. FIGS. 13A to 13C and 14A to 14C are graphs ofthe light transmittance of the LCD devices with respect to the voltageapplied thereto (transmittance vs. applied voltage characteristics):FIGS. 13A and 14A show the results obtained when measured from the upperside; FIGS. 13B and 14B show the results obtained when measured from theright side; and FIGS. 13C and 14C show the results obtained whenmeasured from the left side.

[0422] Referring to FIGS. 13A to 13C, curves L21 c, L24 c, and L27 c(the one-dot dash lines) represent sample #51c which uses a liquidcrystal material with Δn(550) of 0.070 for the liquid crystal layer 8,curves L22 c, L25 c, and L28 c (the solid lines) represent sample #52cwhich uses a liquid crystal material with Δn(550) of 0.080 for theliquid crystal layer 8, and curves L23 c, L26 c, and L29 c (the dashedlines) represent sample #53c which uses a liquid crystal material withΔn(550) of 0.095 for the liquid crystal layer 8.

[0423] Referring to FIGS. 14A to 14C, curves L30 c, L32 c, and L34 c(the solid lines) represent comparative sample #601c which uses a liquidcrystal material with Δn(550) of 0.060 for the liquid crystal layer 8,and curves L31 c, L33 c, and L35 c (the dashed lines) represent sample#602c which uses a liquid crystal material with Δn(550) of 0.120 for theliquid crystal layer 8.

[0424] As for the transmittance vs. applied voltage characteristicsmeasured from the upper side, as shown by curves L21 c to L23 c in FIG.13A, it was confirmed that in samples #51c to #53c as the voltageincreased the transmittance sufficiently decreased. On the contrary, incomparative sample #602c, as shown by-curve L31 c in FIG. 14A, as thevoltage increased the transmittance did not sufficiently decrease. Incomparative sample #601c, as shown by curve L30 c in FIG. 14A, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0425] Likewise, as for the transmittance vs. applied voltagecharacteristics measured from the right side, as shown by curves L24 cto L26 c in FIG. 13B, it was confirmed that in samples #51c to #53c asthe voltage increased the transmittance decreased to nearly zero. Incomparative sample #601c, as shown by curve L32 c in FIG. 14B, as thevoltage increased the transmittance decreased to nearly zero. However,in comparative sample #602c, as shown by curve L33 c in FIG. 14B, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0426] Likewise, as for the transmittance vs. applied voltagecharacteristics measured from the left side, as shown by curves L27 c toL29 c in FIG. 13C, it was confirmed that in samples #51c to #53c as thevoltage increased the transmittance decreased to nearly zero. Incomparative sample #601c, as shown by curve L34 c in FIG. 14C, as thevoltage increased the transmittance decreased to nearly zero. However,in comparative sample #602c, as shown by curve L35 c in FIG. 14C, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0427] From the above results shown in FIGS. 13A to 13C for the samplesof the LCD device of this example (samples #51c to #53c) using, for theliquid crystal layer 8, a liquid crystal material of which the values ofthe refractive index anisotropy Δn(550) for light with a wavelength of550 nm were set at 0.070, 0.080, and 0.095, it is recognized that an LCDdevice with a wide angle of field and an excellent viewing anglecharacteristic without an occurrence of an inversion phenomenon can berealized.

[0428] On the contrary, as shown in FIGS. 14A to 14C, as for thecomparative samples of the LCD devices (comparative samples #601c and#602c) using liquid crystal materials of which the values of therefractive index anisotropy Δn(550) for 550 nm light were set at 0.060and 0.120, an inversion phenomenon occurred and the transmittance duringthe application of a voltage was not sufficiently decreased, notreaching a level tolerable for use.

[0429] The dependence of the transmittance vs. applied voltagecharacteristics on the tilt angle θ was examined by changing the tiltangle θ of the index ellipsoid of the optical phase plate 2 or 3. As aresult, it was found that the optical compensation effect of the opticalphase plate for the liquid crystal layer is ensured when the tilt angleis in the range of 15°≦θ≦75°.

[0430] If the tilt angle is less than 15° or exceeds 75°, the angle offield is not widened, thereby failing to obtain a sufficient viewingangle characteristic. Especially, with such a tilt angle, the angle offield tends to be narrowed in the negative viewing direction.

[0431] The dependence of the transmittance vs. applied voltagecharacteristics on the second retardation value (na−nb)×d was examinedby changing the second retardation value of the optical phase plates 2and 3. As a result, it was found that the optical compensation effect ofthe optical phase plate for the liquid crystal layer is ensured when thesecond retardation value is in the range between 80 nm and 250 nminclusive.

[0432] If the second retardation value (na−nb)×d is less than 80 nm orexceeds 250 nm, the angle of field is not widened, thereby failing toobtain a sufficient viewing angle characteristic. Especially, with sucha second retardation value, the angle of field tends to be narrowed inthe right and left directions.

EXAMPLE 15

[0433] In Example 15, three samples (samples #1c to #3c) of the LCDdevice shown in FIG. 10 were produced in the following manner. OptomerAL, manufactured by Japan Synthetic Rubber Co., Ltd., was used for thealignment films 11 and 14. The cell thickness of the liquid crystal cell16 of these samples was 5 μm. The division ratio of liquid crystalmolecule orientation domains of the portion of the liquid crystal layer8 corresponding to one pixel region (first liquid crystal moleculeorientation domain 8 a: second liquid crystal molecule orientationdomain 8 b) was set at 6:4, 17:3, and 19:1 for samples #1c to #3c,respectively. The rates of variation of the ordinary light refractiveindex no and the extraordinary light refractive index ne of each samplewere set as shown in Table 15 below. TABLE 15 Sample #1c #2c #3c #101c(ne(450) − ne(550))/(ne(550) − ne(650)) 1.35 1.50 1.60 1.85 (no(450) −no(550))/(no(550) − no(650)) 1.15 1.30 1.45 1.85

[0434] As the optical phase plates 2 and 3, those including a discoticliquid crystal material in a tilted orientation as in Example 10 wereused.

[0435] Using the measurement system shown in FIG. 5 including thelight-receiving element 18, the amplifier 19, and the recording device20, an experiment was performed to examine how the division ratio of thefirst liquid crystal molecule orientation domain 8 a to the secondliquid crystal molecule orientation domain 8 b in one pixel regionaffects the viewing angle characteristic.

[0436] In the measurement system, the liquid crystal cell 16 of the LCDdevice to be measured was placed in the measurement system, as inExample 14, so that the surface 16 a of the glass substrate 9 of theliquid crystal cell 16 was in the reference plane x-y of the rectangularcoordinate system xyz. The light-receiving element 18 capable ofreceiving light at a constant solid light-receiving angle was positionedat a predetermined distance from the origin of the coordinate system ina direction of an angle φ (viewing angle) from the z-axis which isnormal to the surface 16 a of the liquid crystal cell 16.

[0437] In the measurement, the surface opposite to the surface 16 a ofthe liquid crystal cell 16 placed in the measurement system wasirradiated with monochrome light with a wavelength of 550 nm. Part ofthe monochrome light which had passed through the liquid crystal cell 16was incident on the light-receiving element 18. The output of thelight-receiving element 18 was amplified to a predetermined level by theamplifier 19, and then recorded by the recording device 20 including awaveform memory, a recorder, and the like.

[0438] The LCD devices of samples #1c to #3c were placed in the abovemeasurement system, to measure the relationship between the voltageapplied to the LCD devices and the output level of the light-receivingelement 18 when the light-receiving element 18 was fixed at a constantangle φ.

[0439] It was assumed that the x-axis direction is toward the lower sideof the screen and the y-axis direction is toward the left side thereof.The measurement was performed by changing the position of thelight-receiving element 18 among positions at an angle φ of 30° in theupward direction (negative viewing direction), the downward direction(positive viewing direction), the right direction, and the leftdirection.

[0440] The results of the above measurements are shown in FIGS. 15A to15C. FIGS. 15A to 15C are graphs of the light transmittance of the LCDdevices with respect to the voltage applied thereto (transmittance vs.applied voltage characteristics): FIG. 15A shows the measurement resultsof sample #1c having the division ratio of the liquid crystal moleculeorientation domains in one pixel region of 6:4; FIG. 15B shows themeasurement results of sample #2c having the division ratio of 17:3; andFIG. 15C shows the measurement results of sample #3c having the divisionratio of 19:1.

[0441] In FIGS. 15A to 15C, curve L1 c (represented by the solid line)shows the characteristics measured in the z-axis direction, curve L2 c(represented by the broken line) shows the characteristics measured fromthe lower side, curve L3 c (represented by the dotted line) shows thecharacteristics measured from the right side, curve L4 c (represented bythe one-dot dash line) shows the characteristics measured from the upperside, and curve L5 c (represented by the two-dot dash line) shows thecharacteristics measured from the left side.

[0442] As is observed from FIG. 15B, in sample #2c, having the divisionratio of 17:3, curves L2 c to L5 c are close to curve L1 c in thetransmittance vs. applied voltage characteristics in the gray scaledisplay region. This indicates that in the gray scale display regionsubstantially the same viewing angle characteristic can be obtained inwhichever direction, the upward, downward, right, or left direction, theviewing angle is tilted.

[0443] In the measurement from the lower side, the transmittance waskept at a low value of about 7% in the ON state, with no inversionphenomenon observed. In the measurement from the upper side, thetransmittance was lower than that measured from the lower side in the ONstate, indicating that the transmittance was sufficiently decreased.

[0444] Substantially the same improvement in the viewing anglecharacteristic as that described above was recognized in sample #1cshown in FIG. 15A and sample #3c shown in FIG. 15C.

[0445] For example, as shown in FIG. 15A, in sample #1c having thedivision ratio of 6:4, the tendency that curve L2 c (measured from thelower side) is close to curve L4 c (measured from the upper side) in thegray scale display region in the ON state appears. This tendency becomeslarger as the division ratio is larger. Also, as shown in FIG. 15C, insample #3c having the division ratio of 19:1, the tendency that curve L2c (measured from the lower side) is close to curve L1 c (measured in thez-axis direction) in the gray scale display region in the ON stateappears. This tendency becomes larger as the division ratio is smaller.This suppresses the phenomenon of destroying black scale of displayimages when viewed from the lower side (in the positive viewingdirection).

[0446] As a result of further detailed examination, it has beenconfirmed that, when the division ratio of the liquid crystal moleculeorientation domains in one pixel region is in the range of 7:3 to 9:1, agood viewing angle characteristic balanced between views from the upperand lower sides can be obtained.

[0447] For comparison, comparative sample #101c having the divisionratio of the first liquid crystal molecule orientation domain 8 a to thesecond liquid crystal molecule orientation domain 8 b in the liquidcrystal layer 8 of 1:1 was produced, and the viewing angle dependencethereof was measured using the measurement system shown in FIG. 5. Themeasurement results are shown in FIG. 16.

[0448] In FIG. 16, curve L11 c (represented by the solid line) shows thecharacteristics measured in the z-axis direction, curve L12 c(represented by the broken line) shows the characteristics measured fromthe lower side, curve L13 c (represented by the dotted line) shows thecharacteristics measured from the right side, curve L14 c (representedby the one-dot dash line) shows the characteristics measured from theupper side, and curve L15 c (represented by the two-dot dash line) showsthe characteristics measured from the left side.

[0449] As is-observed from FIG. 16, the transmittance was sufficientlylow in the ON state when measured from the right and left sides, havingno problem in the viewing angle characteristic. However, when measuredfrom the upper and lower sides, the transmittance was not sufficientlydecreased in the ON state, indicating the existence of the viewing angledependence in the upward and downward directions.

[0450] In this embodiment, two optical phase plates 2 and 3 weredisposed on the surfaces of the LCD element 1. The viewing anglecharacteristics as described above can also be obtained by disposing theoptical phase plate on either one surface of the LCD element 1. In thecase of a single optical phase plate, however, although the viewingangle characteristic in the upward and downward directions are balancedand improved, the viewing angle characteristic in the right and leftdirections may sometimes become asymmetrical. In the case of two opticalphase plates, not only the viewing angle characteristic in the upwardand downward directions are improved as in the case of the singleoptical phase plate, but also the viewing angle characteristics in theright and left directions become symmetrical and improved. In the caseof two optical phase plates, both optical phase plates may be disposedon either one surface of the LCD element 1 in a manner of one on top onthe other. It is also possible to use three or more optical phaseplates.

[0451] (Embodiment 4)

[0452] The LCD device of Embodiment 4 has substantially the sameconfiguration as that in Embodiment 3. In Embodiment 3, the rates ofvariation of the ordinary light refractive index no and theextraordinary light refractive index ne of the liquid crystal materialwith respect to the wavelength are set in a range in which viewing angledependent coloring does not occur on the display screen. Instead, inEmbodiment 4, in consideration of the matching with the wavelengthdependence of the refractive index of the optical phase plates 2 and 3,the conditions of the combination of the length of an average alkylchain of the liquid crystal material, the rate of variation of theordinary light refractive index no of the liquid crystal material withrespect to the wavelength, and rate of variation of the extraordinarylight refractive index ne of the liquid crystal material with respect tothe wavelength are set so that viewing angle dependent coloring does notoccur on the display screen.

[0453] More specifically, the conditions of the combination of thelength of a mean alkyl chain of the liquid crystal material, the rate ofvariation of the ordinary light refractive index no of the liquidcrystal material with respect to the wavelength, and the rate ofvariation of the extraordinary light refractive index ne of the liquidcrystal material with respect to the wavelength are set so as to satisfyat least any one of settings (1) to (3) below.

[0454] (1) In the case where the length m of a mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is m<3.40, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range:1.00 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ −0.422m + 2.55.

[0455] More preferably, the rates of variation are set in the followingrange:1.00 ≤ (no(450) − no(550))/(no(550) − no(650))/(ne(450) − ne(550))/(ne(550) − ne(650)) ≤ −0.343m + 2.26.

[0456] (2) In the case where the length m of the mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is 3.40≦m≦3.90, the rateof variation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range:0.80 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.20.

[0457] More preferably, the rates of variation are set in the followingrange:0.85 < (no(450) − no(550))/(no(550) − no(650))/(ne(450) − ne(550))/(ne(550) − ne(650)) < 1.15.

[0458] (3) In the case where the length m of the mean alkyl chain(C_(m)H_(2m+1)—) of the liquid crystal material is m>3.90, the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in thefollowing range:−0.422m + 2.55 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0459] More preferably, the rates of variation are set in the followingrange:−0.343  m + 2.26 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0460] By utilizing the above ranges, in the LCD device of thisembodiment, high-quality display images with a wide angle of fieldwithout coloring when the viewing angle is dropped or during gray scaledisplay are obtained.

[0461] Hereinbelow, the LCD device of this embodiment will be describedby way of specific examples.

EXAMPLE 16

[0462] In Example 16, in the LCD device shown in FIG. 10, a liquidcrystal material for the liquid crystal layer 8 was obtained by blendingthe materials represented by structural formula (4) below:

[0463] so that the length m of a mean alkyl chain (C_(m)H_(2m+1)—) permole is m>3.90, and that the rate of variation among the extraordinarylight refractive indices ne(450), ne(550), and ne(650) of the liquidcrystal material for light with wavelengths of 450 nm, 550 nm, and 650nm, respectively, and the rate of variation among the ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are in therange of: $\begin{matrix}{{{{- 0.422}\quad m} + 2.55} \leq {\left( {\left( {{{no}(450)} - {{no}(550)}} \right)/\left( {{{no}(550)} - {{no}(650)}} \right)} \right)/\left( {\left( {{{ne}(450)} - {{ne}(550)}} \right)/\left( {{{ne}(550)} - {{ne}(650)}} \right)} \right)} \leq {1.00.}} & (E)\end{matrix}$

[0464] For the alignment films 11 and 14, Optomer AL, manufactured byJapan Synthetic Rubber Co., Ltd., was used. The division ratio of thefirst liquid crystal molecule orientation domain 8 a to the secondliquid crystal molecule orientation domain 8 b of the portion of theliquid crystal layer 8 corresponding to one pixel region was set at17:3. The cell thickness of the liquid crystal cell 16 (the thickness ofthe liquid crystal layer 8) was set at 5 μm. Five samples of such LCDdevices as shown in Table 16 below (samples #11d to #15d) were produced.In Table 16, as well as Tables 17 to 20 for Examples 17 to 20, to bedescribed later, F{no(λ), ne(λ)} represents the following:F{no(λ), ne(λ)} = ((no(540) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650)))

[0465] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis in the xyz coordinate systemand the direction of the principal refractive index nc is tilted byabout 20° in the direction of the arrow B from the x-axis.

[0466] For comparison, two comparative samples of LCD devices as shownin Table 16 below (comparative samples #201d and #202d) were produced inthe same manner as that in the above samples of this example, exceptthat liquid crystal materials having a value of F{no(λ), ne(λ)} whichwas outside the above range (E) were used for the liquid crystal layer 8of the LCD device shown in FIG. 10.

[0467] Table 16 shows the results of visual inspections of color hue atviewing angles of 50°, 60°, and 70° performed for samples #11d to #15dand comparative samples #201d and #202d. In Table 16 as well as Tables17 and 18 for Examples 17 and 18, to be described later, the mark ◯represents “no coloring”, Δ represents “tolerable coloring”, and Xrepresents “intolerable coloring”. TABLE 16 Sample #201d #11d #12d #13d#14d #15d #202d Mean alkyl chain 4.60 5.00 4.20 4.60 4.50 5.00 4.75length (m) F{no(λ), ne(λ)} 0.50 0.44 0.80 0.70 0.89 1.00 1.10 Viewingangle (θ) 50° x ∘ ∘ ∘ ∘ ∘ x 60° x x Δ ∘ ∘ ∘ x 70° x x x ∘ ∘ ∘ x

[0468] It is found from Table 16 that in samples #13d to #15d nocoloring was observed even when the viewing angle was dropped to 70°,providing good image quality. This indicates that especially excellentcharacteristics are provided in the range of:−0.343  m + 2.26 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.

[0469] As for samples #11d and #12d, although coloring was observed atviewing angles of 60° and 70°, no coloring was observed at an viewingangle of 50° or less, providing good display characteristics of a leveltolerable for use.

[0470] As for comparative samples #201d and #202d, however, coloring waseminently observed when the viewing angle is dropped to 50°, providingdisplay characteristics of a level intolerable for use.

EXAMPLE 17

[0471] In Example 17, in the LCD device shown in FIG. 10, a liquidcrystal material for the liquid crystal layer 8 was obtained by blendingthe materials shown in Example 16, so that the length m of the meanalkyl chain (C_(m)H_(2m+1)—) per mole is m<3.40, and that the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) of the liquid crystal material for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, are set in the range of: $\begin{matrix}{1.00 \leq {\left( {\left( {{{no}(450)} - {{no}(550)}} \right)/\left( {{{no}(550)} - {{no}(650)}} \right)} \right)/\left( {\left( {{{ne}(450)} - {{ne}(550)}} \right)/\left( {{{ne}(550)} - {{ne}(650)}} \right)} \right)} \leq {{{- 0.422}\quad m} + {2.55.}}} & (F)\end{matrix}$

[0472] For the alignment films 11 and 14, Optomer AL, manufactured byJapan Synthetic Rubber Co., Ltd., was used. The division ratio of thefirst liquid crystal molecule orientation domain 8 a to the secondliquid crystal molecule orientation domain 8 b of the portion of theliquid crystal layer 8 corresponding to one pixel region was set at17:3. The cell thickness of the liquid crystal cell 16 (the thickness ofthe liquid crystal layer 8) was set at 5 μm. Five samples of such LCDdevices as shown in Table 17 below (samples #21d to #25d) were produced.

[0473] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis in the xyz coordinate systemand the direction of the principal refractive index nc is tilted byabout 20° in the direction of the arrow B from the x-axis.

[0474] For comparison, two comparative samples of LCD devices as shownin Table 17 below (comparative samples #301d and #302d) were produced inthe same manner as that in the above samples of this example, exceptthat liquid crystal materials having a value of F{no(λ), ne(λ)} whichwas outside the above range (F) were used for the liquid. crystal layer8 of the LCD device shown in FIG. 10.

[0475] Table 17 shows the results of visual inspections of color hue atviewing angles of 50°, 60°, and 70° performed for samples #21d to #25dand comparative samples #301d and #302d. TABLE 17 Sample #301d #21d #22d#23d #24d #25d #302d Mean alkyl chain 3.38 3.30 3.25 3.30 3.38 3.35 3.30length (m) F{no(λ), ne(λ)} 1.25 1.14 1.16 1.13 1.05 1.00 0.90 Viewingangle (θ) 50° x ∘ ∘ ∘ ∘ ∘ x 60° x Δ Δ ∘ ∘ ∘ x 70° x x x ∘ ∘ ∘ x

[0476] It is found from Table 17 that in samples #23d to #25d nocoloring was observed even when the viewing angle was dropped to 70°,providing good image quality. This indicates that especially excellentcharacteristics are provided in the range of:1.00 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ −0.343  m + 2.26.

[0477] As for samples #21d and #22d, although coloring was observed atviewing angles of 60° and 70°, no coloring was observed at an viewingangle of 50° or less, providing good display characteristics of a leveltolerable for use.

[0478] As for comparative samples #301d and #302d, however, coloring waseminently observed when the viewing angle is dropped to50°, providingdisplay characteristics of a level intolerable for use.

EXAMPLE 18

[0479] In Example 18, in the LCD device shown in FIG. 10, a liquidcrystal material for the liquid crystal layer 8 was obtained by blendingthe materials shown in Example 16, so that the length m of the meanalkyl chain (C_(m)H_(2m+1)—) per mole is 3.40≦m≦3.90, and that the rateof variation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) of the liquid crystal material for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, are set in the range of: $\begin{matrix}{0.80 \leq {\left( {\left( {{{no}(450)} - {{no}(550)}} \right)/\left( {{{no}(550)} - {{no}(650)}} \right)} \right)/\left( {\left( {{{ne}(450)} - {{ne}(550)}} \right)/\left( {{{ne}(550)} - {{ne}(650)}} \right)} \right)} \leq {1.20.}} & (G)\end{matrix}$

[0480] For the alignment films 11 and 14, Optomer AL, manufactured byJapan Synthetic Rubber Co., Ltd., was used. The division ratio of thefirst liquid crystal molecule orientation domain 8 a to one pixel regionto the second liquid crystal molecule orientation domain 8 b of theportion of the liquid crystal layer 8 corresponding was set at 17:3. Thecell thickness of the liquid crystal cell 16 (the thickness of theliquid crystal layer 8) was set at 5 μm. Five samples of such LCDdevices as shown in Table 18 below (samples #31d to #35d) were produced.

[0481] The optical phase plates 2 and 3 were formed in the followingmanner. A discotic liquid crystal material was applied to a transparentsupport (made of triacetyl cellulose (TAC), for example). The discoticliquid crystal material was crosslinked in a tilted orientation so thatthe first retardation value (nc−na)×d is 0 nm while the secondretardation value (na−nb)×d is 100 nm, and that the tilt angle θ of atilted index ellipsoid is 20° where the direction of the principalrefractive index nb shown in FIG. 3 is tilted by about 20° in thedirection of the arrow A from the z-axis in the xyz coordinate systemand the direction of the principal refractive index nc is tilted byabout 20° in the direction of the arrow B from the x-axis.

[0482] For comparison, two comparative samples of LCD devices as shownin Table 18 below (comparative samples #401d and #402d) were produced inthe same manner as that in the above samples of this example except thatliquid crystal materials having a value of F{no(λ), ne(λ)} which wasoutside the above range (G) were used for the liquid crystal layer 8 ofthe LCD device shown in FIG. 10.

[0483] Table 18 shows the results of visual inspections of color hue atviewing angles of 50°, 60°, and 70° performed for samples #31d to #35dand comparative samples #401d and #402d. TABLE 18 Sample #401d #31d #32d#33d #34d #35d #402d Mean alkyl chain 3.90 3.55 3.80 3.68 3.60 3.45 3.40length (m) F{no(λ), ne(λ)} 0.75 0.85 0.90 1.00 1.10 1.15 1.25 Viewingangle (θ) 50° x ∘ ∘ ∘ ∘ ∘ x 60° x Δ ∘ ∘ ∘ Δ x 70° x x ∘ ∘ ∘ x x

[0484] It is found from Table 18 that in samples #32d to #34d nocoloring was observed even when the viewing angle was dropped to 70°,providing good image quality. This indicates that especially excellentcharacteristics are provided in the range of:0.85⟨((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.15.

[0485] As for samples #31d and #35d, although coloring was observed atviewing angles of 60° and 70°, no coloring was observed at an viewingangle of 500 or less, providing good display characteristics of a leveltolerable for use.

[0486] As for comparative samples #401d and #402d, however, coloring waseminently observed when the viewing angle was dropped to 50°, providingdisplay characteristics of a level intolerable for use.

EXAMPLE 19

[0487] In Example 19, three samples (samples #41d to #43d) of the LCDdevice shown in FIG. 10 were produced in the following manner. OptomerAL, manufactured by Japan Synthetic Rubber Co., Ltd., was used for thealignment films 11 and 14. Liquid crystal materials of which the valuesof the refractive index anisotropy Δn(550) for light with a wavelengthof 550 nm were set at 0.070, 0.080, and 0.095, respectively, were usedfor the liquid crystal layer 8. The division ratio of liquid crystalmolecule orientation domains of the portion of the liquid crystal layer8 corresponding to one pixel region was set at 17:3. The cell thicknessof the liquid crystal cell 16 of these samples was 5 μm. In each sample,the length m of the mean alkyl chain and the value of F{no(λ), ne(λ)}were set as shown in Table 19 below. TABLE 19 Sample #501d #41d #42d#43d #502d Mean alkyl chain length (m) 4.50 3.30 3.38 3.68 4.60 F{no(λ),ne(λ)} 0.89 1.13 1.05 1.00 0.70

[0488] As the optical phase plates 2 and 3, those including a discoticliquid crystal material in a tilted orientation as in Example 16 wereused.

[0489] For comparison, two comparative samples of LCD devices(comparative samples #501d and #502d) were produced in the same manneras that used in the above samples of this example, except that liquidcrystal materials of which the values of the refractive index anisotropyΔn for light with a wavelength of 550 nm were set at 0.060 and 0.120,respectively.

[0490] The LCD devices of samples #41d to #43d and comparative samples#501d and #502d were measured for the viewing angle dependence using themeasurement system as shown in FIG. 5 described above including thelight-receiving element 18, the amplifier 19, and the recording device20.

[0491] The LCD devices of samples #41d to #43d and comparative samples#501d and #502d were placed in the above measurement system, to measurethe relationship between the voltage applied to the LCD devices and theoutput level of the light-receiving element 18 when the light-receivingelement 18 was fixed at a constant angle φ.

[0492] It was assumed that the x-axis direction is toward the lower sideof the screen (positive viewing direction) and the y-axis direction istoward the left side thereof. The measurement was performed by changingthe position of the light-receiving element 18 among positions at anangle φ of 50° in the upward direction (negative viewing direction), theright direction, and the left direction.

[0493] The measurement results of samples #41d to #43d are shown inFIGS. 17A to 17C, while those of comparative samples #501d and #502d areshown in FIGS. 18A to 18C. FIGS. 17A to 17C and 18A to 18C are graphs ofthe light transmittance of the LCD devices with respect to the voltageapplied thereto (transmittance vs. applied voltage characteristics):FIGS. 17A and 18A show the results obtained when measured from the upperside; FIGS. 17B and 18B show the results obtained when measured from theright side; and FIGS. 17C and 18C show the results obtained whenmeasured from the left side.

[0494] Referring to FIGS. 17A to 17C, curves L21 d, L24 d, and L27 d(the one-dot dash lines) represent sample #41d which uses a liquidcrystal material with Δn(550) of 0.070 for the liquid crystal layer 8,curves L22 d, L25 d, and L28 d (the solid lines) represent sample #42dwhich uses a liquid crystal material with Δn(550) of 0.080 for theliquid crystal layer 8, and curves L23 d, L26 d, and L29 d (the dashedlines) represent sample #43d which uses a liquid crystal material withΔn(550) of 0.095 for the liquid crystal layer 8.

[0495] Referring to FIGS. 18A to 18C, curves L30 d, L32 d, and L34 d(the solid lines) represent comparative sample #501d which uses a liquidcrystal material with Δn(550) of 0.060 for the liquid crystal layer 8,and curves L31 d, L33 d, and L35 d (the dashed lines) represent sample#502d which uses a liquid crystal material with Δn(550) of 0.120 for theliquid crystal layer 8.

[0496] As for the transmittance vs. applied voltage characteristicsmeasured from the upper side, as shown by curves L21 d to L23 d in FIG.17A, it was confirmed that in samples #41d to #43d as the voltageincreased the transmittance sufficiently decreased. On the contrary, incomparative sample #502d, as shown by curve L31 d in FIG. 18A, as thevoltage increased the transmittance did not sufficiently decrease. Incomparative sample #501d, as-shown by curve L30 d in FIG. 18A, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0497] Likewise, as for the transmittance vs. applied voltagecharacteristics measured from the right side, as shown by curves L24 dto L26 d in FIG. 17B, it was confirmed that in samples #41d to #43d asthe voltage increased the transmittance decreased to nearly zero. Incomparative sample #501d, as shown by curve L32 d in FIG. 18B, as thevoltage increased the transmittance decreased to nearly zero. However,in comparative sample #502d, as shown by curve L33 d in FIG. 18B, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0498] Likewise, as for the transmittance vs. applied voltagecharacteristics measured from the left side, as shown by curves L27 d toL29 d in FIG. 17C, it was confirmed that in samples #41d to #43d as thevoltage increased the transmittance decreased to nearly zero. Incomparative sample #501d, as shown by curve L34 d in FIG. 18C, as thevoltage increased the transmittance decreased to nearly zero. However,in comparative sample #502d, as shown by curve L35 d in FIG. 18C, as thevoltage increased, the transmittance initially decreased and thenincreased again, causing an inversion phenomenon.

[0499] From the above results shown in FIGS. 17A to 17C for the samplesof the LCD device of this example (samples #41d to #43d) using, for theliquid crystal layer 8, a liquid crystal material of which the values ofthe refractive index anisotropy Δn(550) for light with a wavelength of550 nm were set at 0.070, 0.080, and 0.095, it is recognized that an LCDdevice with a wide angle of field and excellent viewing anglecharacteristic without an occurrence of an inversion phenomenon can berealized.

[0500] On the contrary, as shown in FIGS. 18A to 18C, as for thecomparative samples of the LCD devices (comparative samples #501d and#502d) using liquid crystal materials of which the values of therefractive index anisotropy Δn(550) for 550 nm light were set at 0.060and 0.120, an inversion phenomenon occurred and the transmittance duringthe application of a voltage was not sufficiently decreased, notreaching a level tolerable for use.

[0501] The dependence of the transmittance vs. applied voltagecharacteristics on the tilt angle θ was examined by changing the tiltangle θ of the index ellipsoid of the optical phase plate 2 or 3. As aresult, it was found that the optical compensation effect of the opticalphase plate for the liquid crystal layer is ensured when the tilt angleis in the range of 15°≦θ≦75°.

[0502] If the tilt angle is less than 15° or exceeds 75°, the angle offield is not widened thereby failing to obtain a sufficient viewingangle characteristic. Especially, with such a tilt angle, the angle offield tends to be narrowed in the negative viewing direction.

[0503] The dependence of the transmittance vs. applied voltagecharacteristics on the second retardation value (na−nb)×d was examinedby changing the second retardation value of the optical phase plates 2and 3. As a result, it was found that the optical compensation effect ofthe optical phase plate for the liquid crystal layer is ensured when thesecond retardation value is in the range between 80 nm and 250 nm,inclusive.

[0504] If the second retardation value (na−nb)×d is less than 80 nm orexceeds 250 nm, the angle of field is not widened, thereby failing toobtain a sufficient viewing angle characteristic. Especially, with sucha second retardation value, the angle of field tends to be narrowed inthe right and left directions.

EXAMPLE 20

[0505] In Example 20, three samples (samples #1d to #3d) of the LCDdevice shown in FIG. 10 were produced in the following manner. OptomerAL, manufactured by Japan Synthetic Rubber Co., Ltd., was used for thealignment films 11 and 14. The cell thickness of the liquid crystal cell16 of these samples was 5 μm. The division ratio of liquid crystalmolecule orientation domains of each portion of the liquid crystal layer8 corresponding to each pixel region (first liquid crystal moleculeorientation domain 8 a: second liquid crystal molecule orientationdomain 8 b) was set at 6:4, 17:3, and 19:1 for samples #1d to #3d,respectively. The means alkyl chain length m of the liquid crystalmaterial and the value of F{no(λ), ne(λ)} were set as shown in Table 20below. TABLE 20 Sample #1d #2d #3d #101d Mean alkyl chain length (m)3.30 3.38 3.68 4.50 F{no(λ), ne(λ)} 1.13 1.05 1.00 0.89

[0506] As the optical phase plates 2 and 3, those including a discoticliquid crystal material in a tilted orientation as in Example 16 wereused.

[0507] Using the measurement system shown in FIG. 5 including thelight-receiving element 18, the amplifier 19, and the recording device20, an experiment was performed to examine how the division ratio of thefirst liquid crystal molecule orientation domain 8 a to the secondliquid crystal molecule orientation domain 8 b in one pixel regionaffects the viewing angle characteristic.

[0508] In the measurement system, the liquid crystal cell 16 of the LCDdevice to be measured was placed in the measurement system, as inExample 19, so that the surface 16 a of the glass substrate 9 of theliquid crystal cell 16 was in the reference plane x-y of the rectangularcoordinate system xyz. The light-receiving element 18 capable ofreceiving light at a constant solid light-receiving angle was positionedat a predetermined distance from the origin of the coordinate system ina direction of an angle φ (viewing angle) from the z-axis which isnormal to the surface 16 a of the liquid crystal cell 16.

[0509] In the measurement, the surface opposite to the surface 16 a ofthe liquid crystal cell 16 placed in the measurement system wasirradiated with monochrome light with a wavelength of 550 nm. Part ofthe monochrome light which had passed through the liquid crystal cell 16was incident on the light-receiving element 18. The output of thelight-receiving element 18 was amplified to a predetermined level by theamplifier 19, and then recorded by the recording device 20 including awaveform memory, a recorder, and the like.

[0510] The LCD devices of samples #1d to #3d were placed in the abovemeasurement system, to measure the relationship between the voltageapplied to the LCD devices and the output level of the light-receivingelement 18 when the light-receiving element 18 was fixed at a constantangle φ.

[0511] It was assumed that the x-axis direction is toward the lower sideof the screen and the y-axis direction is toward the left side thereof.The measurement was performed by changing the position of thelight-receiving element 18 among positions at an angle φ of 30° in theupward direction (negative viewing direction), the downward direction(positive viewing direction), the right direction, and the leftdirection.

[0512] The results of the above measurements are shown in FIGS. 19A to19C. FIGS. 19A to 19C are graphs of the light transmittance of the LCDdevices with respect to the voltage applied thereto (transmittance vs.applied voltage characteristics): FIG. 19A shows the measurement resultsof sample #1d having the division ratio of the liquid crystal moleculeorientation domains in one pixel region of 6:4; FIG. 19B shows themeasurement results of sample #2d having the division ratio of 17:3; andFIG. 19d shows the measurement results of sample #3d having the divisionratio of 19:1.

[0513] In FIGS. 19A to 19C, curve L1 d (represented by the solid line)shows the characteristics measured in the z-axis direction, curve L2 d(represented by the broken line) shows the characteristics measured fromthe lower side, curve L3 d (represented by the dotted line) shows thecharacteristics measured from the right side, curve L4 d (represented bythe one-dot dash line) shows the characteristics measured from the upperside, and curve L5 d (represented by the two-dot dash line) shows thecharacteristics measured from the left side.

[0514] As is observed from FIG. 19B, in sample #2d, having the divisionratio of 17:3, curves L2 d to L5 d are close to curve L1 d in thetransmittance vs. applied voltage characteristics in the gray scaledisplay region. This indicates that in the gray scale display regionsubstantially the same viewing angle characteristic can be obtained inwhichever direction, the upward, downward, right, or left direction, theviewing angle is tilted.

[0515] In the measurement from the lower side, the transmittance waskept at a low value of about 7% in the ON state, with no inversionphenomenon observed. In the measurement from the upper side, thetransmittance was lower than that measured from the lower side in the ONstate, indicating that the transmittance was sufficiently increased.

[0516] Substantially the same improvement in the viewing anglecharacteristic as that described above was recognized in sample #1dshown in FIG. 19A and sample #3d shown in FIG. 19C.

[0517] For example, as shown in FIG. 19A, in sample #1d having thedivision ratio of 6:4, the tendency that curve L2 d (measured from thelower side) is close to curve L4 d (measured from the upper side) in thegray scale display region in the ON state appears. This tendency becomeslarger as the division ratio is larger. Also, as shown in FIG. 19C, insample #3d having the division ratio of 19:1, the tendency that curve L2d (measured from the lower side) is close to curve L1 d (measured in thez-axis direction) in the gray scale display region in the ON stateappears. This tendency becomes larger as the division ratio is smaller.This suppresses the problem of destroying black scale of display imageswhen viewed from the lower side (in the positive viewing direction).

[0518] As a result of further detailed examination, it has beenconfirmed that, when the division ratio of the liquid crystal moleculeorientation domains in one pixel region is in the range between 7:3 and9:1, a good viewing angle characteristic balanced between views from theupper and lower sides can be obtained as sample #3d having the divisionratio of 7:3 described above.

[0519] For comparison, comparative sample #101d having the divisionratio of the first liquid crystal molecule orientation domain 8 a to thesecond liquid crystal molecule orientation domain 8 b in the liquidcrystal layer 8 of 1:1 was produced, and the viewing angle dependencethereof was measured using the measurement system shown in FIG. 5. Themeasurement results are shown in FIG. 20.

[0520] In FIG. 20, curve L11 d (represented by the solid line) shows thecharacteristic measured in the z-axis direction, curve L12 d(represented by the broken line) shows the characteristic measured fromthe lower side, curve L13 d (represented by the dotted line) shows thecharacteristic measured from the right side, curve L14 d (represented bythe one-dot dash line) shows the characteristic measured from the upperside, and curve L15 d (represented by the two-dot dash line) shows thecharacteristic measured from the left side.

[0521] As is observed from FIG. 20, the transmittance was sufficientlylow in the ON state when measured from the right and left sides, havingno problem in the viewing angle characteristic. However, when measuredfrom the upper and lower sides, the transmittance was not sufficientlydecreased in the ON state, indicating the existence of the viewing angledependence in the upward and downward directions.

[0522] In this embodiment, two optical phase plates 2 and 3 weredisposed on the surfaces of the LCD element 1. The viewing anglecharacteristics as described above can also be obtained by disposing theoptical phase plate on either one surface of the LCD element 1. In thecase of a single optical phase plate, however, although the viewingangle characteristics in the upward and downward directions are balancedand improved, the viewing angle characteristics in the right and leftdirections may sometimes become asymmetrical. In the case of two opticalphase plates, not only the viewing angle characteristics in the upwardand downward directions are improved as in the case of the singleoptical phase plate, but also the viewing angle characteristics in theright and left directions become symmetrical and improved. In the caseof two optical phase plates, both optical phase plates may be disposedon either one surface of the LCD element 1 in a manner of one on top onthe other. It is also possible to use three or more optical phaseplates.

[0523] In the above description, each of the first liquid crystalmolecule orientation domain 8 a and the second liquid crystal moleculeorientation domain 8 b of one pixel region is shown to be formed as onecontinuous domain as shown in FIG. 11, for example. Substantially thesame effect can also be obtained by orienting the molecules so that thedomain appears discontinuously. For example, the molecules may beoriented so that the first liquid crystal molecule orientation domain 8a appears in two portions, the upper and lower portions of one pixel,sandwiching the second liquid crystal molecule orientation domain 8 b.In such an arrangement of discontinuous domains, the division ratio ofthe total area of the first liquid crystal molecule orientation domainto the total area of the second liquid crystal molecule orientationdomain of one pixel is preferably in the range between 6:4 and 19:1,inclusive. The optimal arrangement of the first liquid crystal moleculeorientation domain and the second liquid crystal molecule orientationdomain of one pixel is determined depending on the size of the pixel andgeneration of a disclination line at the boundary of the domains.

[0524] In order to obtain a maximum effect in widening the angle offield, a percentage closest to 100% of all the pixel regions included inone LCD device are preferably divided into a plurality of liquid crystalmolecule orientation domains. In actual fabrication, the LCD device isformed so that all pixel regions included in the LCD device have aplurality of liquid crystal molecule orientation domains.

[0525] Thus, as described above, according to the present invention, aphase plate as follows is used. That is, the three principal refractiveindices na, nb, and nc of the index ellipsoid of the phase plate havethe relationship of na=nc>nb. The direction of the principal refractiveindex nb is tilted clockwise or counterclockwise from the normal of thesurface of the phase plate with respect to the direction of one of theprincipal refractive indices na and nc which is substantially parallelto the surface of the phase plate as an axis. At the same time, thedirection of the other principal refractive index nc or na is tiltedclockwise or counterclockwise from the direction substantially parallelto the surface of the phase plate. By using such a phase plate, a changein the phase difference of the LCD device can be compensated. Inaddition, at least one of the rates of variation of the ordinary lightrefractive index no and the extraordinary light refractive index ne ofthe liquid crystal material for the liquid crystal layer with respect tothe wavelength may be set in the range in which viewing angle dependentcoloring does not occur. By utilizing these settings, such viewing angledependent coloring can be further prevented. Moreover, the inversionphenomenon and the reduction in the contrast ratio in the negativeviewing direction can be further reduced, compared with the case ofusing only the compensation function of the phase plate.

[0526] According to the present invention, a phase plate as follows isused. That is, the three principal refractive indices na, nb, and nc ofthe index ellipsoid of the phase plate have the relationship ofna=nc>nb. The direction of the principal refractive index nb is tiltedclockwise or counterclockwise from the normal of the surface of thephase plate with respect to the direction of one of the principalrefractive indices na and nc which is substantially parallel to thesurface of the phase plate as an axis. At the same time, the directionof the other principal refractive index nc or na is tilted clockwise orcounterclockwise from the direction substantially parallel to thesurface of the phase plate. By using such a phase plate, a change in thephase difference of the LCD device can be compensated. In addition, theconditions of the combination of the mean alkyl chain length of theliquid crystal material for the liquid crystal layer, the rate ofvariation of the ordinary light refractive index no of the liquidcrystal material with respect to the wavelength, and the rate ofvariation of the extraordinary light refractive index ne of the liquidcrystal material with respect to the wavelength may be set in the rangein which viewing angle dependent coloring does not occur. By utilizingthese settings, such viewing angle dependent coloring can be furtherprevented. Moreover, the inversion phenomenon and the reduction in thecontrast ratio in the negative viewing direction can be further reduced,compared with the case of using only the compensation function of thephase plate.

[0527] According to the present invention, the LCD element in which theportion of the liquid crystal layer corresponding to one pixel region isdivided into a plurality of liquid crystal molecule orientation domainshaving different orientation states at an unequal division ratio may becombined with a negative uniaxial optical phase element of which indexellipsoid is tilted. By this combination, the angle of field can bewidened in the upward and downward directions (12 o'clock-6 o'clockdirections) of the display screen, as well as in the right and leftdirections (3 o'clock-9 o'clock directions). In particular, for a viewfrom the upper side (in the negative viewing direction), thetransmittance during the application of a voltage can be sufficientlylowered. For a view from the lower side (in the positive viewingdirection), the phenomenon of destroying black scale during theapplication of a voltage can be made less conspicuous.

[0528] Moreover, at least one of the rates of variation of the ordinarylight refractive index no and the extraordinary light refractive indexne of the liquid crystal material with respect to the wavelength may beoptimized. By this optimization, coloring on the display screen observedwhen the viewing angle is dropped or during gray scale display can bereduced. Alternatively, the conditions of the combination of the meanalkyl chain length of the liquid crystal material, and the rates ofvariation of the ordinary light refractive index no and theextraordinary light refractive index ne of the liquid crystal materialwith respect to the wavelength may be optimized. By this optimization,also, coloring on the display screen observed when the viewing angle isdropped or during gray scale display can be reduced. Thus, an LCD devicehaving display characteristics of a wide angle of field, high contrast,and excellent visibility having no coloring on the display screen can berealized.

[0529] According to the present invention, it is taken intoconsideration that there are liquid crystal materials which aredifferent in the range of the rate of variation of the refractive indexwith respect to the wavelength in which viewing angle dependent screencoloring does not occur. Based on this consideration, for each of thecases that the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00,

[0530] and the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00,

[0531] the range suitable for each case is set. By utilizing theseranges, viewing angle dependent coloring can be further prevented.Moreover, the inversion phenomenon and the reduction in the contrastratio in the negative viewing direction can be further reduced, comparedwith the case of using only the compensation function of the phaseplate.

[0532] When the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00,

[0533] at least one of the rates of variation of the ordinary lightrefractive index no and the extraordinary light refractive index ne ofthe liquid crystal material with respect to the wavelength may beoptimized. By this optimization, coloring on the liquid crystal displayscreen can be reduced to a level tolerable for use when viewed in anydirection at a viewing angle of 60° which is larger than the viewingangle required for a normal LCD device, i.e., 50°. In the case of an LCDdevice where the portion of the liquid crystal layer corresponding toone pixel region is divided into a plurality of liquid crystal moleculeorientation domains having different orientation states at an unequaldivision ratio, display characteristics having excellent visibilitywithout any coloring can be realized even when the viewing angle isdropped to 50°.

[0534] Furthermore, by optimizing at least one of the rates of variationof the ordinary light refractive index no and the extraordinary lightrefractive index ne, an LCD device which has a wider angle of field of aviewing angle of 70° can realize display characteristics of excellentvisibility having no coloring phenomenon on the liquid crystal displayscreen when viewed in any direction.

[0535] When the rate of variation among the extraordinary lightrefractive indices ne(450), ne(550), and ne(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, and the rate ofvariation among the ordinary light refractive indices no(450), no(550),and no(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00,

[0536] at least one of the rates of variation of the ordinary lightrefractive index no and the extraordinary light refractive index ne ofthe liquid crystal material with respect to the wavelength may beoptimized. By this optimization, coloring on the liquid crystal displayscreen can be reduced to a level tolerable for use when viewed in anydirection at a viewing angle of 60° which is larger than the viewingangle required for a normal LCD device, i.e., 50°. In the case of an LCDdevice where the portion of the liquid crystal layer corresponding toone pixel region is divided into a plurality of liquid crystal moleculeorientation domains having different orientation states at an unequaldivision ratio, display characteristics having excellent visibilitywithout any coloring even when the viewing angle is dropped to 50° canbe realized.

[0537] Furthermore, by optimizing at least one of the rates of variationof the ordinary light refractive index no and the extraordinary lightrefractive index ne, an LCD device which has a wider angle of field of aviewing angle of 70° can realize display characteristics of excellentvisibility having no coloring phenomenon on the liquid crystal displayscreen when viewed in any direction.

[0538] The conditions of the combination of the mean alkyl chain lengthof the liquid crystal material, and the rates of variation of theordinary light refractive index no and the extraordinary lightrefractive index ne of the liquid crystal material with respect to thewavelength may be optimized. By this optimization, coloring on theliquid crystal display screen can be reduced to a level tolerable foruse when viewed in any direction at a viewing angle of 50° which is aviewing angle required for a normal LCD device. In the case of an LCDdevice where the portion of the liquid crystal layer corresponding toone pixel region is divided into a plurality of liquid crystal moleculeorientation domains having different orientation states at an unequaldivision ratio, display characteristics of excellent visibility havingno coloring even when the viewing angle is dropped to 50° can berealized.

[0539] Furthermore, by optimizing the conditions of the combination ofthe mean alkyl chain length of the liquid crystal material, and therates of variation of the ordinary light refractive index and theextraordinary refractive index of the liquid crystal material withrespect to the wavelength, an LCD device which has a wider angle offield of a viewing angle of 70° can realize display characteristics ofexcellent visibility having no coloring phenomenon on the liquid crystaldisplay screen when viewed in any direction.

[0540] As a result, according to the present invention, since thecontrast ratio in monochrome display is not affected by the viewingangle of an observer, the quality of display images of the LCD devicecan be markedly improved.

[0541] By setting of the refractive index anisotropy Δn(550) for lightwith a wavelength of 550 nm in the range of:

0.060<Δn(550)<0.120

[0542] a phase difference generated in the LCD device depending on theviewing angle can be eliminated. This makes possible to further reduce,not only coloring occurring on the liquid crystal display screendepending on the viewing angle, but also a change in contrast and theinversion phenomenon in the right and left directions. In the case of anLCD device where the portion of the liquid crystal layer correspondingto one pixel region is divided into a plurality of liquid crystalmolecule orientation domains having different orientation states at anunequal division ratio, the transmittance during the application of avoltage can be sufficiently decreased, and the inversion phenomenon andthe reduction in the contrast ratio can be reliably prevented.

[0543] By setting of the refractive index anisotropy Δn(550) for lightwith a wavelength of 550 nm in the range of:

0.070≦Δn(550)≦0.095

[0544] a phase difference generated in the LCD device depending on theviewing angle can be further effectively eliminated. This furtherensures that viewing angle dependent coloring occurring on the liquidcrystal display screen, a change in contrast, and the inversionphenomenon in-the right and left directions can be reduced. In the caseof an LCD device where the portion of the liquid crystal layercorresponding to one pixel region is divided into a plurality of liquidcrystal molecule orientation domains having different orientation statesat an unequal division ratio, the transmittance during the applicationof a voltage can be further sufficiently decreased, and the inversionphenomenon and the reduction in the contrast ratio can be reliablyprevented.

[0545] By setting the tilt angle of the index ellipsoid in the rangebetween 15° and 75°, inclusive, the phase difference compensationfunction of the optical phase element for the liquid crystal layer isreliably obtained. Accordingly, an LCD device having displaycharacteristics of improved visibility, a wide angle of field, and highcontrast can be realized.

[0546] By setting the product of the difference between the principalrefractive indices na and nb of the optical phase element and thethickness d of the optical phase element, i.e., (na−nb)×d in the rangebetween 80 nm and 250 nm, inclusive, the phase difference compensationfunction of the optical phase element for the liquid crystal layer canbe reliably obtained. Accordingly, an LCD device having displaycharacteristics of improved visibility, a wide angle of field, and highcontrast can be realized.

[0547] The LCD element and the optical phase element may be arranged sothat the alignment direction of the alignment film is opposite to thetilt direction of the principal refractive indices nb and no of theoptical phase element in the largest liquid crystal molecule orientationdomain in one pixel region. By this arrangement, the direction in whichliquid crystal molecules rise when a voltage is applied and the tiltdirection of the index ellipsoid of the optical phase element areopposite to each other. This ensures that optical anisotropy generatedat the rising of liquid crystal molecules is compensated by the opticalphase element, and thus an LCD device having display characteristics ofa wide angle of field and high contrast can be realized.

[0548] The LCD element and the optical phase element may be arranged sothat the alignment direction of the alignment film is the same as thetilt direction of the principal refractive indices nb and no of theoptical phase element in the smallest liquid crystal moleculeorientation domain in one pixel region. By this arrangement, thesmallest liquid crystal molecule orientation domain provides the viewingangle characteristic opposite to that of the largest liquid crystalmolecule orientation domain. With the addition of this viewing anglecharacteristic component, the problem of destroying black scale in thelargest liquid crystal molecule orientation domain can be made lessconspicuous, and thus the angle of field in the upward and downwarddirections can be widened.

[0549] By setting the division ratio of the first liquid crystalmolecule orientation domain to the second liquid crystal moleculeorientation domain of the portion of liquid crystal layer correspondingto one pixel region in the range between 6:4 and 19:1 inclusive, theangle of field in the right and left direction can be widened, thecontrast in the upward direction (negative viewing direction) can beimproved, and the phenomenon of destroying black scale duringapplication of a voltage can be suppressed. As a result, an LCD devicehaving a wide angle of field, high contrast, and excellent visibilitycan be realized.

[0550] According to the present invention, an LCD device with a wideangle of field, high display quality, and excellent colorreproducibility is realized. Accordingly, the present invention is veryeffective for a TN mode LCD device in which liquid crystal molecules inthe liquid crystal layer are twisted about 90° between the pair ofsubstrates.

[0551] Various other modifications will be apparent to and can bereadily made by those skilled in the art without departing from thescope and spirit of this invention. Accordingly, it is not intended thatthe scope of the claims appended hereto be limited to the description asset forth herein, but rather that the claims be broadly construed.

What is claimed is:
 1. A liquid crystal display device comprising: aliquid crystal display element including a pair of substrates, a liquidcrystal layer interposed between the pair of substrates, and analignment film formed on a surface of at least one of the pair ofsubstrates facing the liquid crystal layer; a pair of polarizersdisposed on both surfaces of the liquid crystal element to sandwich theliquid crystal element; and at least one optical phase element disposedbetween at least one of the pair of polarizers and the liquid crystalelement, wherein three principal refractive indices na, nb, and nc of anindex ellipsoid of the optical phase element have the relationship ofna=nc>nb, a direction of the principal refractive index nb is tiltedclockwise or counterclockwise from the normal of a surface of theoptical phase element with respect to a direction of one of theprincipal refractive indices na and nc which is substantially parallelto the surface of the optical phase element as an axis, and a directionof the other principal refractive index nc or na is tilted clockwise orcounterclockwise from a direction substantially parallel to the surfaceof the optical phase element, and at least one of rates of variation ofan ordinary refractive index no and an extraordinary refractive index neof a liquid crystal material of the liquid crystal layer with respect toa wavelength is set in a range in which viewing angle dependent coloringdoes not occur on a screen.
 2. A liquid crystal display devicecomprising: a liquid crystal display element including a pair ofsubstrates, a liquid crystal layer interposed between the pair ofsubstrates, and an alignment film formed on a surface of at least one ofthe pair of substrates facing the liquid crystal layer: a pair ofpolarizers disposed on both surfaces of the liquid crystal element tosandwich the liquid crystal element; and at least one optical phaseelement disposed between at least one of the pair of polarizers and theliquid crystal element, wherein three principal refractive indices na,nb, and nc of an index ellipsoid of the optical phase element have therelationship of na=nc>nb, a direction of the principal refractive indexnb is tilted clockwise or counterclockwise from the normal of a surfaceof the optical phase element with respect to a direction of one of theprincipal refractive indices na and nc which is substantially parallelto the surface of the optical phase element as an axis, and a directionof the other principal refractive index nc or na is tilted clockwise orcounterclockwise from a direction substantially parallel to the surfaceof the optical phase element, and conditions of the combination of alength of a mean alkyl chain of a liquid crystal material of the liquidcrystal layer, a rate of variation of an ordinary refractive index no ofthe liquid crystal material with respect to a wavelength, and a rate ofvariation of an extraordinary refractive index ne of the liquid crystalmaterial with respect to a wavelength are set in a range in whichviewing angle dependent coloring does not occur on a screen.
 3. A liquidcrystal display device according to claim 1, further comprising aplurality of pixel regions for displaying, wherein at least one of theplurality of pixel regions is divided into a first liquid crystalmolecule orientation domain and a second liquid crystal moleculeorientation domain which have different orientation states of liquidcrystal molecules included in the liquid crystal layer, and the area ofthe first liquid crystal molecule orientation domain is larger than thearea of the second liquid crystal molecule orientation domain.
 4. Aliquid crystal display device according to claim 2, further comprising aplurality of pixel regions for displaying, wherein at least one of theplurality of pixel regions is divided into a first liquid crystalmolecule orientation domain and a second liquid crystal moleculeorientation domain which have different orientation states of liquidcrystal molecules included in the liquid crystal layer, and the area ofthe first liquid crystal molecule orientation domain is larger than thearea of the second liquid crystal molecule orientation domain.
 5. Aliquid crystal display device according to claim 1, wherein the rate ofvariation among extraordinary light refractive indices ne(450), ne(550),and ne(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, and the rate of variation among ordinary light refractiveindices no(450), no(550), and no(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, have the relationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≥ 1.00.


6. A liquid crystal display device according to claim 1, wherein therate of variation among the ordinary light refractive indices no(450),no(550), and no(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, is set in a range of:1.65≦(no(450)−no(550))/(no(550)−no(650))≦2.40.
 7. A liquid crystaldisplay device according to claim 6, wherein the rate of variation amongthe ordinary light refractive indices no(450), no(550), and no(650) forlight with wavelengths of 450 nm, 550 nm, and 650 nm, respectively, isset in a range of: 1.85≦(no(450)−no(550))/(no(550)−no(650))≦2.20.
 8. Aliquid crystal display device according to claim 1, wherein the rate ofvariation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, is set in a range of:1.70≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.30.
 9. A liquid crystaldisplay device according to claim 8, wherein the rate of variation amongthe extraordinary light refractive indices ne(450), ne(550), and ne(650)for light with wavelengths of 450 nm, 550 nm, and 650 nm, respectively,is set in a range of: 1.85≦(ne(450)−ne(550))/(ne(550)−ne(650))≦2.10. 10.A liquid crystal display device according to claim 1, wherein the rateof variation among extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, and the rate of variation among ordinary lightrefractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, have therelationship of:((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) < 1.00.


11. A liquid crystal display device according to claim 1, wherein therate of variation among the ordinary light refractive indices no(450),no(550), and no(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, is set in a range of:1.00≦(no(450)−no(550))/(no(550)−no(650))≦1.65.
 12. A liquid crystaldisplay device according to claim 11, wherein the rate of variationamong the ordinary light refractive indices no(450), no(550), andno(650) for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, is set in a range of:1.15≦(no(450)−no(550))/(no(550)−no(650))≦1.45.
 13. A liquid crystaldisplay device according to claim 1, wherein the rate of variation amongthe extraordinary light refractive indices ne(450), ne(550), and ne(650)for light with wavelengths of 450 nm, 550 nm, and 650 nm, respectively,is set in a range of: 1.20≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.70. 14.A liquid crystal display device according to claim 13, wherein the rateof variation among the extraordinary light refractive indices ne(450),ne(550), and ne(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, is set in a range of:1.35≦(ne(450)−ne(550))/(ne(550)−ne(650))≦1.60.
 15. A liquid crystaldisplay device according to claim 2, wherein the length m of the meanalkyl chain (C_(m)H_(2m+1)—) of the liquid crystal material is set in arange of m<3.40, and the rate of variation among extraordinary lightrefractive indices ne(450), ne(550), and ne(650) of the liquid crystalmaterial for light with wavelengths of 450 nm, 550 nm, and 650 nm,respectively, and the rate of variation among ordinary light refractiveindices no(450), no(550), and no(650) for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, are set in a range of:$\begin{matrix}{1.00 \leq {\left( {\left( {{{no}(450)} - {{no}(550)}} \right)/\left( {{{no}(550)} - {{no}(650)}} \right)} \right)/\left( {\left( {{{ne}(450)} - {{ne}(550)}} \right)/\left( {{{ne}(550)} - {{ne}(650)}} \right)} \right)} \leq {{{- 0.422}\quad m} + {2.55.}}} & \quad\end{matrix}$


16. A liquid crystal display device according to claim 15, wherein therate of variation among the extraordinary light refractive indicesne(450), ne(550), and ne(650) of the liquid crystal material for lightwith wavelengths of 450 nm, 550 nm, and 650 nm, respectively, and therate of variation among the ordinary light refractive indices no(450),no(550), and no(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, are set in a range of:1.00 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ −0.343  m + 2.26.


17. A liquid crystal display device according to claim 2, wherein thelength m of the mean alkyl chain (C_(m)H_(2m+1)—) of the liquid crystalmaterial is set in a range of 3.40≦m≦3.90, and the rate of variationamong extraordinary light refractive indices ne(450), ne(550), andne(650) of the liquid crystal material for light with wavelengths of 450nm, 550 nm, and 650 nm, respectively, and the rate of variation amongordinary light refractive indices no(450), no(550), and no(650) forlight with wavelengths of 450 nm, 550 nm, and 650 nm, respectively, areset in a range of: $\begin{matrix}{0.80 \leq {\left( {\left( {{{no}(450)} - {{no}(550)}} \right)/\left( {{{no}(550)} - {{no}(650)}} \right)} \right)/\left( {\left( {{{ne}(450)} - {{ne}(550)}} \right)/\left( {{{ne}(550)} - {{ne}(650)}} \right)} \right)} \leq {1.20.}} & \quad\end{matrix}$


18. A liquid crystal display device according to claim 17, wherein therate of variation among the extraordinary light refractive indicesne(450), ne(550), and ne(650) of the liquid crystal material for lightwith wavelengths of 450 nm, 550 nm, and 650 nm, respectively, and therate of variation among the ordinary light refractive indices no(450),no(550), and no(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, are set in a range of:0.85 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.15.


19. A liquid crystal display device according to claim 2, wherein thelength m of the mean alkyl chain (C_(m)H_(2m+1)—) of the liquid crystalmaterial is set in a range of m>3.90, and the rate of variation amongextraordinary light refractive indices ne(450), ne(550), and ne(650) ofthe liquid crystal material for light with wavelengths of 450 nm, 550nm, and 650 nm, respectively, and the rate of variation among ordinarylight refractive indices no(450), no(550), and no(650) for light withwavelengths of 450 nm, 550 nm, and 650 nm, respectively, are set in arange of: $\begin{matrix}{{{{- 0.422}\quad m} + 2.55} \leq {\left( {\left( {{{no}(450)} - {{no}(550)}} \right)/\left( {{{no}(550)} - {{no}(650)}} \right)} \right)/\left( {\left( {{{ne}(450)} - {{ne}(550)}} \right)/\left( {{{ne}(550)} - {{ne}(650)}} \right)} \right)} \leq {1.00.}} & \quad\end{matrix}$


20. A liquid crystal display device according to claim 19, wherein therate of variation among the extraordinary light refractive indicesne(450), ne(550), and ne(650) of the liquid crystal material for lightwith wavelengths of 450 nm, 550 nm, and 650 nm, respectively, and therate of variation among the ordinary light refractive indices no(450),no(550), and no(650) for light with wavelengths of 450 nm, 550 nm, and650 nm, respectively, are set in a range of:−0.343  m + 2.26 ≤ ((no(450) − no(550))/(no(550) − no(650)))/((ne(450) − ne(550))/(ne(550) − ne(650))) ≤ 1.00.


21. A liquid crystal display device according to claim 1, wherein avalue of refractive index anisotropy Δn(550) of the liquid crystalmaterial for light with a wavelength of 550 nm is set in a range of:0.060<Δn(550)<0.120.
 22. A liquid crystal display device according toclaim 2, wherein a value of refractive index anisotropy Δn(550) of theliquid crystal material for light with a wavelength of 550 nm is set ina range of: 0.060<Δn(550)<0.120.
 23. A liquid crystal display deviceaccording to claim 21, wherein the value of the refractive indexanisotropy Δn(550) of the liquid crystal material for light with awavelength of 550 nm is set in a range of: 0.070<Δn(550)<0.095.
 24. Aliquid crystal display device according to claim 22, wherein the valueof the refractive index anisotropy Δn(550) of the liquid crystalmaterial for light with a wavelength of 550 nm is set in a range of:0.070<Δn(550)<0.095.
 25. A liquid crystal display device according toclaim 1, wherein a tilt angle of the index ellipsoid of the opticalphase element is set in a range between 15° and 75° inclusive.
 26. Aliquid crystal display device according to claim 2, wherein a tilt angleof the index ellipsoid of the optical phase element is set in a rangebetween 15° and 75° inclusive.
 27. A liquid crystal display deviceaccording to claim 1, wherein the product of the difference between theprincipal refractive indices na and nb of the optical phase element andthe thickness d of the optical phase element, i.e., (na−nb)×d is set ina range between 80 nm and 250 nm inclusive.
 28. A liquid crystal displaydevice according to claim 2, wherein the product of the differencebetween the principal refractive indices na and nb of the optical phaseelement and the thickness d of the optical phase element, i.e.,(na−nb)×d is set in a range between 80 nm and 250 nm inclusive.
 29. Aliquid crystal display device according to claim 3, wherein the liquidcrystal display element and the optical phase element are arranged sothat an alignment direction of the alignment film is opposite to a tiltdirection of the principal refractive indices nb and nc of the opticalphase element in the first liquid crystal molecule orientation domain.30. A liquid crystal display device according to claim 4, wherein theliquid crystal display element and the optical phase element arearranged so that an alignment direction of the alignment film isopposite to a tilt direction of the principal refractive indices nb andnc of the optical phase element in the first liquid crystal moleculeorientation domain.
 31. A liquid crystal display device according toclaim 29, wherein the liquid crystal display element and the opticalphase element are arranged so that the alignment direction of thealignment film is the same as the tilt direction of the principalrefractive indices nb and nc of the optical phase element in the secondliquid crystal molecule orientation domain.
 32. A liquid crystal displaydevice according to claim 30, wherein the liquid crystal display elementand the optical phase element are arranged so that the alignmentdirection of the alignment film is the same as the tilt direction of theprincipal refractive indices nb and nc of the optical phase element inthe second liquid crystal molecule orientation domain.
 33. A liquidcrystal display device according to claim 3, wherein an area ratio ofthe first liquid crystal molecule orientation domain to the secondliquid crystal molecule orientation domain in the at least one pixelregion is set in a range between 6:4 and 19:1 inclusive.
 34. A liquidcrystal display device according to claim 4, wherein an area ratio ofthe first liquid crystal molecule orientation domain to the secondliquid crystal molecule orientation domain in the at least one pixelregion is set in a range between 6:4 and 19:1 inclusive.
 35. A liquidcrystal display device according to claim 1, wherein liquid crystalmolecules in the liquid crystal layer are twisted about 90° between thepair of substrates.
 36. A liquid crystal display device according toclaim 2, wherein liquid crystal molecules in the liquid crystal layerare twisted about 90° between the pair of substrates.